Optical display system and method, active and passive dithering using birefringence, color image superpositioning and display enhancement with phase coordinated polarization switching

ABSTRACT

A display apparatus is disclosed comprising a passive display; a light source to provide illumination of the passive display; a video signal input, wherein in response to a video signal the passive display modulates light from the light source to provide an image, and wherein the intensity of light provided by the light source illuminating the display is controlled based on the video signal and wherein the passive display is capable of displaying a preset range of gray levels and presenting a displayed image in response to the video signal; and a control operable to expand a range of gray levels represented in the video signal across substantially all of preset range of gray levels.

This is a divisional of commonly owned U.S. patent application Ser. No.10/983,403, filed Nov. 8, 2004, now U.S. Pat. No. 7,352,347 which is acontinuation of U.S. patent application Ser. No. 09/676,915, filed Oct.2, 2000, now U.S. Pat. No. 6,816,141; which is a continuation ofcommonly owned U.S. patent application Ser. No. 08/817,846, filed Apr.25, 1997, now U.S. Pat. No. 6,184,969; which is the national stage ofinternational application no. PCT/US95/13722, filed Oct. 25, 1995, whichclaims the benefit under 35 USC §119(e) of U.S. provisional applicationSer. No. 60/001,972, filed Jul. 23, 1995 and which is acontinuation-in-part of commonly owned U.S. patent application Ser. No.08/398,292, filed Mar. 3, 1995, now U.S. Pat. No. 5,715,029; which is acontinuation-in-part of commonly owned U.S. patent application Ser. No.08/392,055, filed Feb. 22, 1995, now U.S. Pat. No. 5,572,341; which is acontinuation-in-part of commonly owned U.S. patent application Ser. No.08/328,375, filed Oct. 25, 1994, now U.S. Pat. No. 5,537,256; all ofwhich are incorporated by reference for all purposes as set forthherein.

CROSS REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS

Reference is made to commonly owned U.S. patent application Ser. No.08/187,262, filed Jan. 25, 1994 (now U.S. Pat. No. 5,717,422 issued Feb.10, 1998); Ser. No. 08/187,050, filed Jan. 25, 1994 (now U.S. Pat. No.5,532,854, issued Jul. 2, 1996); Ser. No. 08/187,163, filed Jan. 25,1994; Ser. No. 08/275,907, filed Jul. 5, 1994 (now U.S. Pat. No.5,519,524, issued May 21, 1996), Ser. No. 08/328,375, filed Oct. 25,1994 (now U.S. Pat. No. 5,537,256, issued Jul. 16, 1996); Ser. No.08/392,055, filed Feb. 22, 1995 (now U.S. Pat. No. 5,572,341, issuedNov. 5, 1996); Ser. No. 08/398,292, filed Mar. 3, 1995 (now U.S. Pat.No. 5,715,029, issued Feb. 3, 1998); Ser. No. 08/295,383, filed Aug. 24,1994 (now U.S. Pat. No. 5,621,572, issued Apr. 15, 1997); Ser. No.08/328,371, filed Oct. 25, 1994 (now U.S. Pat. No. 5,858,589, issuedSep. 15, 1998); Ser. No. 08/383,466, filed Feb. 3, 1995 (now U.S. Pat.No. 5,606,458, issued Feb. 5, 1997); and provisional patent applicationSer. No. 60/002,780 entitled Optical system and method for a headmounted display providing both front and peripheral fields of view andSer. No. 60/002,779 entitled Monocular viewing device with retroreflector display system, telecommunication system, and method, bothfiled Jul. 19, 1995. The entire disclosures thereof hereby areincorporated by reference.

TECHNICAL FIELD

The present invention relates generally, as is indicated, to opticaldisplay system and method, active and passive dithering usingbirefringence, color image super positioning, and display enhancementwith phase coordinated polarization switching. The present inventionalso relates to dithering systems for optical displays and methods, and,more particularly, to passive dithering systems and methods for changingthe location of an optical signal and for improving an optical display.The present invention also relates to the enhancing of optical displaysand methods to enhance such displays, and, more particularly, toenhancing optical displays and methods by coordinating the phase ofswitching light with the dynamic operation of the displayed imagedeveloping device.

BACKGROUND

Dithering systems have been used in a number of technologies in thepast. The objective of a dithering system is to change a characteristicof a particular signal in a periodic (or random) fashion in order toprovide a useful output. As is described in further detail, thedithering system of the invention may be used to change the relativelocation of an optical signal.

The present invention may be used with various types of displays andsystems. Exemplary displays are a CRT (sometimes referred to herein ascathode ray tube) display, a liquid crystal display (sometimes referredto herein as “LCD”), especially those which modulate light transmittedthere through, reflective liquid crystal displays, light emittingdisplays, such as electroluminescent displays, plasma displays and soon.

Conventional optical displays typically display graphic visualinformation, such as computer generated graphics, and pictures generatedfrom video signals, such as from a VCR, from a broadcast televisionsignal, etc.; the pictures may be static or still or they may be movingpictures, as in a movie or in a cartoon, for example. Conventionaldisplays also may present visual information of the alphanumeric type,such as numbers, letters, words, and/or other symbols (whether in theEnglish language or in another language). Visual information viewed by aperson (or by a machine or detector) usually is in the form of visiblelight. Such visible light is referred to as a light signal or an opticalsignal. The term optical signal with which the invention may be usedincludes visible light, infrared light, and ultraviolet light, thelatter two sometimes being referred to as electromagnetic radiationrather than light. The optical signal may be in the form of a singlelight ray, a light beam made up of a plurality of light rays, a lightsignal such as a logic one or a logic zero signal used in an opticalcomputer, for example, or the above-mentioned alphanumeric or graphicstype display. Thus, as the invention is described herein, it is usefulwith optical signals of various types used for various purposes.Therefore, in the present invention reference to optical signal, lightray, light beam, light signal, visual information, etc., may be usedgenerally equivalently and interchangeably.

In an exemplary liquid crystal display sometimes referred to as an imagesource, there usually are a plurality of picture elements, sometimesreferred to as pixels or pels, and these pixels can be selectivelyoperated to produce a visual output in the form of a picture,alphanumeric information, etc. Various techniques are used to providesignals to the pixels. One technique is to use a common electrode on oneplate of a liquid crystal cell which forms the display and an activematrix electrode array, such as that formed by thin film transistors(TFT), on the other plate of the liquid crystal cell. Various techniquesare used to provide electrical signals to the TFT array to cause aparticular type of optical output from respective pixels. Anothertechnique to provide signals to the pixels is to use two arrays ofcrossed electrodes on respective substrates of an LCD; by applying ornot applying a voltage or electric field between a pair of crossedelectrodes, a particular optical output can be obtained.

One factor in determining resolution of a liquid crystal display is thenumber of pixels per unit area of the liquid crystal display. Forexample, Sony Corporation recently announced a 1.35 inch diagonal highresolution liquid crystal display which has 513,000 pixels arranged in480 rows of 1,068 pixels per row.

Another factor affecting resolution is the space between adjacent pixelssometimes referred to “as optical dead space”. Such space ordinarily isnot useful to produce an optical signal output. The space usually isprovided to afford a separation between the adjacent pixels to avoidelectrical communication between them. The space also is provided toaccommodate circuitry, leads, and various electrical components, such ascapacitors, resistors, and even transistors or parts of transistors. Theproportion of optical dead space to useful space of pixels that canproduce optical output tends to increase as the physical size of theimage source is decreased, for the space required to convey electricalsignals, for example, may remain approximately constant although theactual size of the useful space of the pixels to produce optical outputcan be reduced because of anticipated image magnification. However, uponmagnification of the image produced by such a miniature image sourceboth the optical dead space and the useful optical space of the pixelsare magnified. Thus, resolution tends to be decreased, especially uponsuch magnification.

The picture elements (pixels or pels) may be discrete pixels, blocks orareas where an optical signal can be developed by emission, reflection,transmission, etc. such as the numerous pixels in the miniature imagesource of Sony Corporation mentioned above. The optical signal referredto may mean that light is “on” or provided as an output from the device,or that the pixel has its other condition of not producing or providinga light output, e.g., “off”; and the optical signal also may be variousbrightness's of light or shades of gray. Alternatively, the opticaloutput or optical signal produced by a pixel may be a color or light ofa particular color.

The pixels may be a plurality of blocks or dots arranged in a number oflines or may be a number of blocks or dots randomly located or groupedin a pattern on the display or image source (source of the opticalsignal). The pixels may be a number of lines or locations along theraster lines that are scanned in a CRT type device or the pixels may beone or a group of phosphor dots or the like at particular locations,such as along a line in a CRT or other device. The optical signalproduced by one or more pixels may be the delivery of light from thatpixel or the non-delivery of light from that pixel, or variousbrightness's or shades of gray. To obtain operation of a pixel, forexample, the pixel may be energized or not. In some devices energizingthe pixel may cause the pixel to provide a light output, and in otherdevices the non-energizing of the pixel may cause the providing of alight output; and the other energized condition may cause the oppositelight output condition. It also is possible that the nature of the lightoutput may be dependent on the degree of energization of a pixel, suchas by providing the pixel with a relatively low voltage or relativelyhigh voltage to obtain respective optical output signals (on and off oroff and on, respectively).

For example, in a conventional twisted nematic liquid crystal displaydevice, polarized light is received by a liquid crystal cell, anddepending on whether the liquid crystal cell receives or does notreceive a satisfactory voltage input, the plane of polarization of thelight output by the liquid crystal cell will or will not be rotated; anddepending on that rotation (or not) and the relative alignment of anoutput analyzer, light will be transmitted or not. In an optical phaseretardation device that has variable birefringence, such as thosedisclosed in U.S. Pat. Nos. 4,385,806, 4,540,243, and RE.32,521(sometimes referred to as surface mode liquid crystal cells), dependingon the optical phase retardation provided by the liquid crystal cell,plane polarized light may be rotated, and the optical output can bedetermined as a function of the direction of the plane of polarization.In a CRT light emission or not and brightness may be determined byelectrons incident on a phosphor at a pixel. In electroluminescentdisplays and plasma displays light output may be determined byelectrical input at respective areas on pixels.

The interlacing of raster lines or display lines is a known practiceused in television and in other types of display systems. For example,in NTSC and PAL television type cathode ray tube (CRT) displays it isknown that two interlaced fields of horizontal lines are used to providean entire image frame. First one raster or set of lines is scanned tocause one subframe (sometimes referred to as field) to be displayed; andthen a second raster or set of lines is scanned to cause a secondsubframe (field) to be displayed. The electrical signals used to scanone line in one subframe and the electrical signals used to scan therelatively adjacent line of the subsequent subframe may be different,and, therefore, the optical outputs of those lines may be different. Thetwo raster subframes are presented sufficiently fast that the eye of anobserver usually cannot distinguish between the respective images of thetwo successive subframes but rather integrates the two subframes to seea composite image (sometimes referred to as a frame or picture). The twosubframes are created sequentially by “writing” the image to respectivepixels formed by phosphors to which an electron beam may be directed inresponse to electrical signals which control the electron beam in on-offand/or intensity manner. After the electron beam has reached the end ofits scanning to create one subframe, e.g., the last pixel or phosphordot area of that field, there is a period of time while the electronbeam is moved or directed to the first pixel of the next subframe.During that period of time a blanking pulse is provided to preventelectrons from being directed to phosphors or pixels causing undesiredlight emission. Sometimes various circuits of a television or CRTdisplay are synchronized to the operative timing of the television, CRT,etc. by synchronization with such blanking pulses.

The density of pixels, e.g., number of pixels per unit area, in a CRTdisplay usually is, in a sense, an analog function depending oncharacteristics of the electron beam, drive and control circuitry forthe beam, phosphor dot layout, shadow mask(s), etc., as is known.Usually a CRT is driven using the interlaced lines forming the subframesmentioned above. In an LCD, though, there is a fixed number of pixelsper line or row; and data, e.g., whether a given pixel in a row is totransmit light or to block light transmission, usually is written to thepixels a row at a time. The data is written to one row, then to thenext, and so on, and there usually is no interlacing of rows or ofsubframes as there is in CRT driving techniques.

In some LCD's the two subframes mentioned above usually are effectivelyaveraged together, when driven by a CRT type of interlaced signal, sincethere usually is no physical interlacing of LCD pixels to formrespective subframes as there are respective scan lines of phosphordots, for example, in a CRT. Rather, the electrical signals for drivingadjacent scan lines of different respective interlaced subframes of aCRT display, both usually are delivered to only a single row of pixelsin an LCD. Each pixel responds to the electrical signal applied theretoto transmit or to block light, for example. Those two sets of electricalsignals are applied to the row of pixels at different times. Therefore,at one time a given row of LCD pixels may present as an optical outputoptical information from one subframe and at a later time presentoptical information from the other subframe.

Since the optical information presented in one subframe is expected tobe displaced in space from the optical information presented in theother subframe to obtain the interlacing pattern of a CRT display,careful examination of the optical output from the above-mentioned LCDwill show an amount of “jittering” of the image. This jittering iscaused by the pixels of one row periodically being changed so theoptical output thereof sequentially displays the result of energizationby signals representing one scan line of information from one subframeand then energization by electrical signals representing the adjacentscan line of information from the next subframe.

This jittering can degrade the displayed image and can make viewinguncomfortable. Also, the problems, such as viewing discomfort and/orimage degrading, caused by jittering tend to increase as the image isenlarged or magnified, e.g., when the image is created by a relativelyminiature image source, such as the SONY display mentioned above, and ismagnified for direct viewing or for projection by a projector.

One technique for reducing the jittering is to use relatively slowliquid crystal display devices. Therefore, the liquid crystal displayelement or pixel tends to average the electrical signals appliedthereto. A disadvantage to this technique, though, is that imageresolution is reduced because the information representing two scanlines is combined into a single line. Also, a slow acting liquid crystaldisplay element tends to have undesirable hysteresis that slows motionbeing shown by the display.

In a color display, such as a LCD (liquid crystal display), thereusually are red, green and blue pixels which form a color triad(hereinafter referred to as triad). By operating the LCD in such a waythat one or more of the pixels forming a triad provides (or produces)the respective color light of that pixel, different respective colorsand white can be produced as output light. For example, if the red pixelof a triad were providing red output light; and the green and bluepixels were not providing output light, the light output from that triadwould be red. Further, when two or more pixels of a triad are providinglight output, a combination of those colors is seen by a person viewing(sometimes referred to as the viewer) the light output or image. Theviewer usually visually superimposes the output light from the pixels ofthe triad; and the combined or superimposed lights there from providethe net effect or integrated light output of the triad. As an example,to produce a white light output from a triad, the red, green and bluepixels of that triad would provide, respectively, red, green and bluelight; and those lights would be, in effect, superimposed by the viewerand seen as white light.

There is a continuing need and/or desire to improve resolution ofdisplays. It also would be desirable to facilitate the placing ofcircuitry in a display while minimizing the optical dead space caused bythe circuitry. There also is a need to reduce jitter.

In the above-mentioned patent applications are disclosed techniques foractively dithering, moving an optical signal, changing the location oroptical path of an optical signal, etc. for several purposes, such as toincrease resolution, to reduce jitter, and so on. There also aredisclosed techniques for passive dithering, moving of optical signals,etc., for example to increase the fill factor of an image provided by adisplay by expanding the image or pixels forming the image.

An LCD using the twisted nematic effect usually cannot switch betweentransmission states as rapidly as changes occur in the appliedelectrical signal which operates the LCD. For example, the electricalinput to a twisted nematic LCD can change nearly instantly, but it takesa number of milliseconds for the LCD to respond dynamically to thechange in electrical input to change the optical response of the LCD.When an LCD is used in a display system that employs dithering todouble, quadruple or otherwise to change the effective number of pixels,for convenience hereinafter, sometimes referred to as optical linedoubling (or OLD), the relatively slow response of the twisted nematicLCD compared to the faster operation of the dithering optics can resultin an optical output that does not achieve the desired improvement inresolution or other optical effect.

The displaying of a dark scene using a display device (sometimesreferred to as a passive display), which modulates light received from aseparate light source, encounters a disadvantage which ordinarily is notpresent for displays which produce their own light, such as a cathoderay tube (CRT). The problem has to do with reduced resolution and/orcontrast of the displayed image.

In a CRT, for example, when it is desired to display a dark scene, theintensity of the output light can be reduced. The different parts of thedark scene, then, all may be output at the reduced brightness orilluminance level. All pixels (e.g., picture elements, phosphor dots ina monochrome display or group of three red, green and blue phosphor dotsfor a multicolor display, etc.) of the CRT can be active so thatresolution is maintained even though intensity of the light produced bythe phosphors is reduced.

However, in a passive display device, such as a liquid crystal display,an electro chromic display, etc., whether of the light transmitting typeor of the light reflecting type, the usual practice to reduce brightnessof a displayed image or scene is to reduce the number of pixels whichare transmitting light at a particular moment. Such a reduction reducesthe resolution of the display. Also, such a reduction can reduce thecontrast of the display.

The human eye has difficulty distinguishing between seeing orrecognizing the difference between low and high brightness and contrastranges. This difficulty is increased when the number of pixels isdecreased and resolution is degraded.

It would be desirable to improve the contrast and resolution of passivedisplays.

In U.S. patent application Ser. No. 08/187,163 is disclosed a passiveapparatus, such as an LCD, and method for displaying images with highcontrast by controlling the light input to the display to controlbrightness of the output while operating respective pixels of thedisplay to obtain good contrast substantially without regard to theoutput brightness. Different color effects also are disclosed using, forexample, field sequential switching of respective color light. However,this is another example of a passive optical device, in this case anLCD, in which field sequential switching could be improved ifcoordinated with the delays inherent in the dynamic optical response ofa liquid crystal cell, for example, relative to the changes in operatingsignal, such as electric field, voltage, etc.

As is described in application Ser. No. 08/187,163, an image of acandlelit room would be dim. In the prior art devices a relatively smallnumber of pixels would be used, then, to transmit light to create theimage, whereas a relatively large number of pixels would be used toblock light transmission to give the effect of the reduced intensity ordim room. In the invention of such application, though, the number ofpixels used to create the image remains constant, and the contrast ratiobetween one portion and another portion of the image remain constant;only the intensity of the illuminating light changes thereby to diminishthe brightness of the room. Therefore, with the invention image data isnot lost regardless of the brightness of the image, whereas in the priorart image data is lost because the additional pixels are used tobrighten or darken the brightness of the image.

The features of the invention as described in that patent applicationcan be used in a frame sequential basis. The features of the inventioncan be used regardless of whether the display is operated in reflectivemode or in transmissive mode. Also, the features of the invention can beused in a virtual reality type display in order to provide a very widerange of contrast and of image brightness characteristics. The pictureinformation is used to derive the brightness of the display, not thesurrounding ambient. Using the invention of that application, the amountof information that can be conveyed by the display is substantiallyincreased over the prior art.

For example, if there were a grey scale of 100 shades of grey and adisplay with 10 shades of grey, the intensity of the illuminating sourcecan be changed at 10 different levels, for example, and there also canbe 10 different shades of grey provided by the display itself.Therefore, this provides 100 shades of grey. This characteristic can beincreased by another factor of 10 by going to r, g, b (red, green, blue)modulation on a field sequential basis, which allows the possibility of10 to the 6th different illumination levels and colors. The foregoing isespecially important in head mounted displays where immersion in theimage is extremely important. Using features of such patent application,there can be high illumination of the scene, then, the grey scalecontrast ratio of the real image can be adjusted. As a result, there isa high contrast image presented in a bright motif. Another example usingsuch invention is the ability to display a sunrise scene in which thered image is enhanced and the blue and green are minimized.

The invention of that application, then, can separate the two functionsof brightness and image. The image is a function of the operation of theliquid crystal modulator and the illumination brightness is the functionof the light source intensity. The r, g, b colors can be changed to givea candlelight or moonlight effect with good resolution and colorfunction, but the brightness of the scene is a function of thebackground. As a result, it is possible to photograph the scene indaylight to get good contrast; and then by reducing the displayillumination it is possible to give the impression of a moonlit orcandlelit environment.

SUMMARY

With the foregoing in mind, then, one aspect of the invention is toincrease the resolution of a display by electro-optically dithering anoptical signal.

Another aspect relates to use of electro-optical dithering to obtainthree dimensional images, especially using auto-stereoscopic effect.

Another aspect relates to using electro-optical dithering to effect beamswitching of optical signals.

Another aspect is electro-optically to change selectively the locationat which an optical output signal is presented to another location. Afurther aspect is to effect such change in more than one direction,e.g., along more then one axis.

According to another aspect, a device for changing or determining thelocation of an optical signal includes birefringent means forselectively refracting light based on optical polarizationcharacteristic of the light, and means for changing such opticalpolarization characteristic of light, the birefringent means and thechanging means being cooperative selectively to change the location ofthe optical signal.

According to another aspect, a system for increasing the resolution ofan optical display having a plurality of picture elements includesbirefringent means for selectively refracting light based onpolarization characteristics of the light, changing means forselectively changing the polarization characteristics of light, and thebirefringent means and the changing means being in optical series andcooperative in response to selective operation of the changing means tochange the location of output optical signals there from.

According to another aspect, a display system includes a display forproducing visual output information by selective operation of aplurality of picture elements at respective locations, and means forchanging the location of the output information as a function of opticalpolarization thereby effectively to increase the number of pictureelements.

According to another aspect, a display system includes a display forproducing visual output information by selective operation of aplurality of picture elements at respective locations, and means forchanging the location of the output information without physicalrealignment of a mechanical device thereby effectively to increase thenumber of picture elements.

According to another aspect, a display system includes a display forproducing visual output information by selective operation of aplurality of picture elements at respective locations, and means forelectro-optically changing the location of the output informationthereby effectively to increase the number of picture elements.

According to another aspect, a method for displaying visual informationincludes presenting a first optical output from a source by providingplural optical signals arranged in a pattern, presenting a secondoptical output from the source by providing plural optical signalsarranged in a pattern, and selectively-shifting the location of thepattern of the second optical output relative to the location of thepattern of the first optical output based on optical polarization.

According to another aspect, an electro-optical dithering system forshifting polarized light includes birefringent means for selectivelyrefracting light as a function of a polarization characteristic of thelight, and changing means for changing the polarization characteristicof polarized light to provide output light that is shifted or not as afunction of optical polarization.

According to another aspect, a method of making a display includespositioning in optical series an image source, a birefringent means forselectively refracting light based on optical polarizationcharacteristic of the light, and a changing means for changing suchoptical polarization characteristic.

Using principles of the invention, the location of an optical signal canbe changed, and the change can be used for a number of purposes. Forexample, the change can be used to improve resolution of a display, toprovide an auto-stereoscopic output, to interlace optical signals, tofacilitate positioning and hiding of circuitry used in a display, tofacilitate overlapping of tiles or pixels in a display, etc. A number ofthese examples are presented below. The invention may be used to achieveone or more of those and other uses.

An aspect of the invention relates to an optical line increaser, whereinthe number of pixels in a optical display can be increased byelectro-optical means.

An aspect of the invention relates to an optical line increaser, whereinthe number of pixels in a optical display can be increased byelectro-optical means, for example, to double, triple, quadruple, orotherwise to increase the effective number of pixels presenting outputoptical information for viewing by a person, machine, other device,etc., and/or for other use.

Another aspect is to hide or to reduce optical dead space in a display.

Another aspect is to use a switchable electro-optical device to effectdithering (changing effective location) of an optical signal.

Another aspect is to reduce jitter in an optical display.

Another aspect is to drive a non-interlaced display using an interlacedsignal and electro-optically dithering the optical output of the displayto reduce jitter.

Another aspect is to increase the effective number of pixels and/orlines of an optical display.

In accordance with a further aspect of the invention, a passivedithering display system includes an optical display including aplurality of pixels with optical dead space between the pixels forproducing an image, and a birefringent material for shifting onepolarization component of the image relative to a second polarizationcomponent of the image such that the shifted polarization component liesin the dead space.

In accordance with another aspect, a display system includes an opticaldisplay for producing an image and a first birefringent material forrefracting one component of the image relative to a second component ofthe image based on polarization characteristics of the components toproduce a plurality of adjacent images.

In accordance with a still further aspect of the invention, a method ofreducing optical background noise includes the steps of displaying aplurality of pixels with optical dead space between said pixels forproducing an image and shifting one polarization component of the imagerelative to a second polarization component of the image such that theshifted polarization component lies in the dead space.

Another aspect relates to expanding an image or pixels of an image toincrease the fill factor of the image, the fill factor relating to theamount of area of the image actually occupied by image compared to thatpart of the image occupied by optical dead space.

Another aspect relates to using passive image or pixel expanding toincrease the fill factor of an image.

Another aspect relates to using active image or pixel doubling (or otherincreasing) to increase fill factor and resolution of an image.

Another aspect relates to techniques to superimpose color pixel imagelight outputs to obtain respective color outputs for a display.

Another aspect is to increase the amount of data able to be displayedfrom a video signal or the like provided to a display system, such as anLCD display system or other display system.

As is described further below, the invention is useful to coordinatelight output by an optical device, such as an LCD, for example, and thedynamic operation of such optical device with another optical device,such as one that switches or shifts the location of the output light foruse, such as viewing, projection, etc., one that displays images infield (sometimes referred to as frame or part of a frame) sequentialoperation to present images with good contrast and/or color effect thatare independent of the brightness of the output light, and so on.

One or more of these and other objects, features and advantages of thepresent invention are accomplished using the invention described andclaimed below.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrativeembodiments of the invention. These embodiments are indicative, however,of but a few of the various ways in which the principles of theinvention may be employed.

Although the invention is shown and described with respect to certainpreferred embodiments, it is obvious that equivalents and modificationswill occur to others skilled in the art upon the reading andunderstanding of the specification. The present invention includes allsuch equivalents and modifications, and is limited only by the scope ofthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 is a schematic side elevation view of a CRT display including anelectro-optical dithering system according to the present invention;

FIG. 2 is a schematic illustration of the components of theelectro-optical dithering system of FIG. 1;

FIG. 3 is a schematic illustration of the double refraction effectthrough a calcite crystal which may be used in the electro-opticaldithering system of the invention;

FIGS. 4A, 4B and 4C are, respectively, schematic illustrationsindicating exemplary axial alignment of the several components of theelectro-optical dithering system shown in FIG. 2;

FIGS. 5A, 5B and 5C are, respectively, schematic illustrations similarto

FIG. 2 showing the operation of the electro-optical dithering system onlight in respective operational modes;

FIG. 6 is a schematic illustration of an alternate embodiment ofelectro-optical dithering system;

FIG. 7 is a schematic front view of the face or display output of a CRTshowing exemplary raster lines;

FIG. 8 is a schematic side elevation view of the electro-opticaldithering system of the invention used in an auto-stereoscopic display;

FIG. 9 is an enlarged view of a single lens element of theauto-stereoscopic display of FIG. 8;

FIG. 10 is a schematic plan view of part of a liquid crystal displayshowing areas where pixels are located and areas where there iscircuitry or dead space located between adjacent pixels and includingthe electro-optical dithering system of the invention;

FIG. 11 is a schematic top view of the display of FIG. 10 showing thepaths of optical signals that are shifted in location according to theon or off state of the electro-optical dithering system of the display;

FIGS. 12 and 13 are schematic block diagrams of synchronizing circuittechniques useful in the various display systems of the invention;

FIGS. 14 and 15A-15E are schematic illustrations of a display system andparts thereof with a double electro-optical dithering system;

FIGS. 16A-16D are schematic illustrations of a pixel pattern that isdithered or not in up to four different spatial pattern locations;

FIG. 17 is a composite of the pixel patterns of FIGS. 16A-16D;

FIGS. 18 and 19 are schematic illustrations of a display system with adouble electro-optical dithering system and parts thereof usingswitchable liquid crystal birefringent devices;

FIG. 20 is a schematic illustration of part of a red, green and bluepixel arrangement for a multicolor display;

FIG. 21 is a schematic illustration of a segmented display system withselective time sequenced dithering of respective segments;

FIGS. 22A-22F are schematic illustrations of the segmented displaysystem of FIG. 21 showing the time sequence of operation thereof;

FIG. 23 is a schematic illustration of a passive dithering system usedin connection with a display which produces a polarized output;

FIG. 24 is a schematic illustration of the effect of dithering in bothhorizontal and vertical directions;

FIG. 25 is a schematic illustration of the orientations of the opticaxes of the components of the passive dithering system of FIG. 23;

FIG. 26 is a schematic illustration of the passive dithering system ofFIG. 23 used in connection with a display which produces a nonpolarized(sometimes referred to as unpolarized) light output;

FIG. 27 is a schematic illustration of the orientations of the opticaxes of the components of the passive dithering system of FIG. 26;

FIG. 28 is a schematic illustration of an alternate embodiment of apassive dithering system;

FIG. 29 is a schematic illustration of the orientations of the opticaxes of the components of the passive dithering system of FIG. 28;

FIG. 30 is a schematic illustration of the passive dithering system ofFIG. 28 used in connection with a display which produces a nonpolarizedlight output;

FIG. 31 is a schematic illustration of an optical display system usingan alternate embodiment of a passive dithering system using unpolarizedlight input;

FIG. 32 is a schematic illustration of the orientations of the opticaxes of the components of the passive dithering system of FIG. 31;

FIG. 33 is a schematic illustration of an alternate embodiment ofoptical display system using an active dithering system for diagonallydisplacing a pixel image;

FIG. 34 is a schematic illustration of the locations of the originalpixel images unshifted and of the shifted pixel images using thedithering system of FIG. 33;

FIG. 35 is a schematic illustration of an alternate embodiment ofoptical display system using active and passive dithering system fordisplacing pixel images;

FIG. 36 is a schematic illustration of the locations of the originalpixel images unshifted and of the shifted pixel images using thedithering system of FIG. 35 in four respective operations;

FIG. 37 is a schematic illustration of the display output from anoptical display system of the type shown in FIG. 35, for example,showing shifting of pixel images relative to each other to obtain superpositioning of color pixel images and increased fill factor;

FIGS. 38 and 39 are schematic illustrations of display outputs from anoptical display system of the type shown in FIG. 35 and or in otherfigures hereof, for example, showing shifting of pixel images into gapsbetween pixels and in overlapping relative to each other;

FIG. 40 is a schematic illustration of the display output from anoptical display system of the type shown in FIG. 41, for example,showing shifting of pixel images according to an exemplary prescribedpattern;

FIG. 41 is a schematic illustration of an optical display systemincluding the components to obtain the operation depicted in FIG. 40 fora head mounted or boom mounted display system or other display system;

FIG. 42 is a schematic illustration of a display system in accordancewith an embodiment of the invention including a head mounted portion;

FIG. 43 is a schematic section elevation view showing the variousoperational parts of the monocular viewing device used in the displaysystem of FIG. 1;

FIG. 44 is a compilation of graphs representing the response of atwisted nematic LCD display pixel when addressed at 60 Hz (Hertz);

FIG. 45 is a compilation of graphs representing the response of atwisted nematic LCD display pixel when addressed at 120 Hz;

FIG. 46 is a compilation of graphs representing the response of asurface mode type birefringent liquid crystal light shutter operating asan optical rotator or switch coordinated with the operation of a twistednematic LCD display pixel which is addressed at 120 Hz;

FIG. 47 is a schematic illustration of a display optical system used inthe viewing device of FIGS. 42-43, for example, and/or in other viewingdevices or display systems disclosed herein;

FIG. 48 is a compilation of graphs showing the relationship of timingsignals for an optical line doubler system that provides both horizontaland vertical doubling (e.g., quadrupling of respective pixels), forexample, as in the embodiment depicted in FIGS. 14-17;

FIG. 49 is a schematic illustration of a light transmissive displaysystem according to an embodiment of the invention;

FIG. 50 is a schematic illustration of a light reflective display systemaccording to an embodiment of the invention;

FIG. 51 is a schematic view of a reflective field sequential display andillumination system using plural cholesteric liquid crystal reflectorsand plural light sources of respective colors to provide a multicolor orfull color display useful in various embodiments of the invention;

FIG. 52 is a schematic view of a head mounted display system including apair of display subsystems in accordance with various embodiments of theinvention; and

FIGS. 53-58 are schematic graphical illustrations depicting operation ofthe invention.

DESCRIPTION

Referring, now in detail to the drawings wherein like reference numeralsdesignate like parts in the several figures and initially to FIG. 1, anelectro-optical dithering system in accordance with an embodiment of thepresent invention is generally indicated at 1 in use with a display 2 toform an optical display system 3 for providing optical signals, visualinformation, etc., as the output there from. The display 2 provides asource of light or optical signals, and such light is transmittedthrough the electro-optical dithering system to provide optical signalsat respective locations for viewing or the like. Exemplary light isrepresented by an arrow 4, such as an optical signal produced at aparticular location by the display 2 or produced by some other sourceand modulated by the display 2 as the output there from.

The location of the output optical signal 5 is represented by arrows 5a, 5 b. Those arrows 5 a, 5 b represent the location of the outputoptical signal 5 resulting from the optical signal 4 being transmittedthrough the electro-optical dithering system 1 while the electro-opticaldithering system is in a respective one or the other of the operativestates thereof, such as off or on.

In the embodiment illustrated in FIG. 1 the display 2 is a CRT. It willbe appreciated that the display 2 may be an LCD or another display, suchas an electroluminescent display, plasma display, flat panel display orother display.

Dithering may refer to the physical displacement of an image. Anelectro-optical dithering system (EDS) refers to an electro-opticalmeans to physically shift, translate or to change the location of anoptical signal, such as an image. The image may be shifted along an axisfrom one location to another and then back to the first, e.g. up andthen down, left and then right, etc. The optical signal may be moved inanother direction along a straight or other axis or not along an axis atall. The dithering may be repetitive or periodic or it may beasynchronous in moving an image from one location to another and thenholding it there, at least for a set or non-predetermined time.

The electro-optical dithering system 1, as it is shown in FIG. 1,includes birefringent material, which sometimes is referred to as doublerefracting material, 10. An example of birefringent material is acalcite crystal material. Other double refracting (birefringent)materials also may be used. Birefringent material may transmit lightstraight through or may refract the light which is incident thereon,depending on a characteristic of the light incident thereon, such asoptical polarization characteristic. In the illustrated embodiment theoptical polarization characteristic is the direction of the electricvector of plane polarized light. Plane polarized light having onedirection of electric vector (sometimes referred to as direction of thepolarization axis, the transmission axis of the polarizer or of thelight, the plane of polarization of the light, the direction ofpolarization, etc.) may transmit directly through the birefringentmaterial 10 without being refracted or bent, whereas light having adifferent direction of plane of polarization may be refracted (bent) bythe birefringent material 10. For example, plane polarized light whichencounters one index of refraction characteristic, such as an ordinaryindex of refraction characteristic, of the birefringent material may betransmitted without refraction. However, plane polarized light whichencounters a different index of refraction characteristic, such as theextraordinary index of refraction, of the birefringent material willbend or refract at the interface with the birefringent material, bothupon entering and upon leaving the birefringent material. Therefore, ina sense the birefringent material 10 changes the direction of lighttransmitted through it, for example, as it changes the location of theoutput optical signal from location 5 a to 5 b.

In the optical display system 3 embodiment illustrated in FIG. 1 theelectro-optical dithering system 1 also includes a switch 11 that can beoperated to change the characteristic of light relevant to thebirefringent material 10 to change the location of the output opticalsignal. In the exemplary embodiment of FIG. 1 refraction of light ortransmission of light without refraction by the birefringent material 10depends on the direction of polarization of plane polarized lightincident on the birefringent material 10, and the switch 11 is able toswitch the direction of polarization of such light incident on thebirefringent material 10.

In the embodiment illustrated in FIG. 1 the switch 11 is a liquidcrystal cell or liquid crystal shutter type device which is able totransmit light to the birefringent material 10 such that the lightincident on the birefringent material has a plane of polarization thatcan be changed by the switch. Accordingly, if the switch is in oneoperative state or mode, the light incident on the birefringent material10 may have a plane of polarization such that the output optical signal5 occurs at the location of the arrow 5 a, and with the switch 11 in adifferent state of energization the plane of polarization of the lightincident on the birefringent material 10 can be changed (e.g., switchedto an orthogonal direction to the first-mentioned plane) thereby tocause the output optical signal to occur at the location of the arrow 5b.

A linear polarizer (sometimes referred to as a plane polarizer) 12 isbetween the switch 11 and the CRT display 2. The light 4 provided by thedisplay 2 is plane polarized by the polarizer 12. The direction ofpolarization in cooperation with one condition of the switch 11 willresult in the light being transmitted directly through the birefringentmaterial 10 without refraction so as to appear at location of arrow 5 a.However, in response to the other condition of the switch 11, the lightwill be refracted by the birefringent material 10 so as to occur at thelocation of the arrow 5 b.

With the foregoing in mind, then, it will be appreciated that theinvention includes a material that can move the location of an outputoptical signal relative to the location of an incident (input) opticalsignal depending on a characteristic of the incident optical signal,such as the direction of plane polarized light. The electro-opticaldithering system 1 of the invention includes birefringent, doublerefracting, or equivalent material and a means to switch or todiscriminate the characteristic of the incident optical signal.

In the embodiment illustrated in FIG. 1, the light 4 from a CRT isunpolarized. The polarizer 12 gives the light a characteristic of linear(plane) polarization. The switch 11 can change the direction ofpolarization, e.g., the direction of the electric vector of thepolarized light. The birefringent material provides the output opticalsignal at the location 5 a, 5 b, depending on the characteristic of thelight incident on the birefringent material.

The switch 11 may be a liquid crystal cell or several liquid crystalcells, such as twisted nematic liquid crystal cells, birefringent liquidcrystal cells, such as those disclosed in U.S. Pat. Nos. 4,385,806,RE.32,521, and 4,540,243, the entire disclosures of which hereby areincorporated by reference. If desired, the liquid crystal cells may bearranged in optical series and operated as a push-pull arrangement toimprove linearity of response, and/or for other purposes, for example,as is disclosed in one or more of the aforementioned patents. Othertypes of liquid crystal cells also may be used for the switch 11.Further, other types of devices that are able to switch the opticalcharacteristic of light, such as the direction of plane polarization,etc., may be used for the switch 11; several examples includeferro-electric liquid crystal cells, variable optical retarders, PLZTdevices, and so on.

An advantage to using a liquid crystal display (LCD) as the display 2with the dithering system 1 is that the output light from an LCD usuallyalready may have a characteristic of optical polarization, such aslinear polarization. In such a case, the linear polarizationcharacteristic provided by such displays may eliminate the need for aseparate linear polarizer 12.

In FIG. 2 the electro-optical dithering system 1 is shown in use in anoptical display system 13 having a transmissive LCD 20. The LCD 20 maybe a twisted nematic liquid crystal display, birefringent liquid crystaldisplay, or some other type of liquid crystal display which produces inresponse to input light 21 from a light source 22, output lightrepresented by an arrow 23. The LCD 20 may be transmissive orreflective. The output light 23 may be, for example, a graphic image,one or more light beams that are selectively turned on or off dependingon operation of the liquid crystal display 20, etc. The graphic imagemay be a moving image, an alphanumeric display, etc. The ditheringsystem 1 includes a birefringent material 10 and a switch 11. Tosimplify the following description, the switch 11 may be referred to asa polarization rotator, which rotates the plane of polarization of thelight represented by arrow 23 an amount depending upon the energizationstate or condition of the polarization rotator. For example, if theswitch 11 were a twisted nematic liquid crystal cell, when it isde-energized, it would rotate the plane of polarization by 90 degrees(or some other amount depending on the nature of the liquid crystalcell), and when the twisted nematic liquid crystal cell is in a fullyenergized condition, it would not rotate the plane of polarization ofthe light incident thereon. Similar operation could be obtained by usingbirefringent liquid crystal cells. Additionally, if desired,compensation may be provided for residual retardation in a liquidcrystal cell, whether of the birefringent or twisted nematic type; suchcompensation may be provided by a wave plate or the like, such as aquarter wave plate positioned in a particular orientation relative tothe rub direction or axis of the liquid crystal cell used in the switch11.

Further, a wave plate, such as a half wave plate, may be used to rotatethe plane of polarization of light 23 so it is appropriately alignedwith the optic axis (sometimes referred to herein as the rub direction,optical axis, or simply axis) of the switch 11. For example, if theswitch 11 were a twisted nematic liquid crystal cell, the plane ofpolarization of the light 23 may be parallel or perpendicular to the rubdirection of one of the plates of the liquid crystal cell. If the switch11 were a birefringent liquid crystal cell, such as a surface mode cellor a pi-cell (e.g., as the above-mentioned patents or in U.S. Pat. No.4,582,396, which is hereby incorporated by reference), the plane ofpolarization of light 23 may be at 45 degrees to the rub direction. Inusing a half wave plate to adjust plane of polarization, for example,the axis of the half wave plate would be aligned to one half the angulardistance between the orientation of the plane of polarization of thelight incident on the half wave plate and the angular orientationdesired for the light output from the half wave plate.

Turning to FIG. 3, there is shown an example of birefringent material 10in the form of the mineral calcite, also referred to as a calcitecrystal 30. Unpolarized light 31 enters the calcite 30 at the left handface 32 thereof. The light enters at a right angle to the face 32. Thelight 31 is resolved into two orthogonally polarized components 33, 34in view of the birefringent nature of the calcite. The optical axis ofthe light components 33, 34 are oriented such that one component 33 hasa plane of polarization or electric vector direction into and out of theplane of the drawing of FIG. 3, as is represented by the dots shown inFIG. 3, and such light 33 experiences an index of refraction changebetween the environment 35 outside the calcite 30 and the environment 36inside the calcite 30. However, the axis of the calcite crystal 30 is ata right angle to the plane of polarization to the light 33, and,therefore, this components of light 33 travels through the calcitecrystal 30 without deflection (refraction); sometimes this light isreferred to herein as the undithered light.

The light component 34 is polarized vertically in the plane of thedrawing of FIG. 3 and is represented by a double-headed arrow in thedrawing. The light component 34 experiences a change in index ofrefraction as above; however, the light component 34 also encounters thecalcite crystal axis at an angle which is other than a right angle.Therefore, the light component 34 is refracted and its path is deflected(direction is changed) as it enters and leaves the crystal on its travelthrough the crystal 30, as is shown in FIG. 3; sometimes this light isreferred to herein as the dithered light. This property of refraction ofone polarization component and no refraction of the other polarizationcomponent of light incident on a birefringent material sometimes iscalled double refraction, and it occurs in many materials. The amount ofphysical displacement between the light components 33, 34 where theyexit the right hand face 37 of the calcite crystal 30 and become,respectively, output light 33 a, 34 a represented by arrows at locations38 a, 38 b, respectively, depends on the thickness of the calcitecrystal, indices of refraction of the calcite crystal and the externalenvironment thereof, and the orientation of the optical axis of thespecific material, as is known.

In the optical display system 3 of FIG. 1 in which the display 2 is aCRT and in the optical display system 13 of FIG. 2 which uses an LCD 20the direction of polarization of light incident on the switch 11 and theorientation of the switch 11 may be related for optimal operation. Inone example of the invention, the switch 11 is a birefringent liquidcrystal cell (or a pair of them operating in push-pull manner), and suchliquid crystal cell(s) has (have) an axis which sometimes is referred toas the rub direction, alignment direction, optic or optical axis, etc.of the liquid crystal cell. Using such a liquid crystal cell in thesystems 3 or 13, for optimal operation the polarization direction(transmission direction axis of the polarizer 12 or of the LCD 20, forexample) should be at 45 degrees relative to the axis of the switch 11.Additionally, preferably the projection of the axis of the calcitecrystal 30 is oriented at 45 degrees to the axis of the switch 11. Theserelationships are depicted in FIGS. 4A, 4B and 4C.

Briefly referring to FIGS. 4A, 4B and 4C, the above-describedrelationships of axes is shown. In FIG. 4A the transmission axis of thepolarizer 12 or the plane of polarization of light delivered by theliquid crystal display 20 or by CRT 2 and polarizer 12 is shown ashorizontal at 40. However, such direction also may be vertical, becauseit is desired that the relationship between that axis and the axis ofthe liquid crystal cell(s) of the birefringent liquid crystal cellswitch 11 be at a relative 45 degrees thereto. Such 45 degreesrelationship is shown by the respective axes 41, 42 for the switch 11.In fact, such axes 41, 42 may represent the axis of one liquid crystalcell and the axis of a second liquid crystal cell, the two beingarranged in optical series and being operated in push-pull fashion. Theaxes 43, 44 of the calcite crystal 30 are shown as horizontal andvertical. However, the vertical axis actually is tipped in or out of theplane of the drawing and it actually is the projection of that axeswhich would appear as vertical; alternatively or additionally thehorizontal axis may be tipped. Such projection of the axes preferably isat 45 degrees to the axes 41, 42 of the switch 11. The describedrelative orientation of the axes of the various components used inconnection with the invention is exemplary, and it will be appreciatedthat other arrangements may be used to obtain a particular type ofoperation. However, in the ideal simplified case described herein, therelationship described may be employed. Also, it will be appreciatedthat compensation may be provided to adjust the effective orientation ofa particular axis. Such compensation can be provided using abirefringent material, a wave plate, such as a quarter wave plate oranother one, etc., as was mentioned above.

It will be appreciated that whether the axis of a birefringent switch 11is at plus or minus 45 degrees, represented by the axis lines 41, 42,for example, and whether a respective axis 43, 44 of the calcite 30 orother double refracting material 10 is at plus or minus 45 degrees tothe axis of the birefringent switch (and parallel or perpendicular tothe plane of polarization 40) will determine whether the ditheredoptical signal will be moved up, down, left or right relative to theundithered signal. If the switch 11 were a twisted nematic liquidcrystal cell, the axis 40 may be parallel or perpendicular to one of theaxes of the liquid crystal cell, and the orientation of the calcite 30may be as shown in FIG. 4C relative to the plane of polarization of thelight represented at 40 in FIG. 4A.

It will be appreciated that the arrangement of axes herein described areexemplary. The alignment of the switch 11, whatever that component iscomprised of, preferably is such that the switch is able to change acharacteristic of light in the display system 3, 13 (and othersdescribed herein, for example) so that selective dithering can becarried out by a double refraction or other functionally equivalentmaterial or device. Orientation of the double refracting material may besuch as to cause such selective dithering depending on an opticalcharacteristic of the light, which is incident thereon and/or istransmitted there through, relative to the double refracting material.

Quarter wave plates, other wave plates, etc. may be used in conjunctionwith coupling of light along optical paths used in the electro-opticaldithering system 1 and/or the optical display systems 3 or 13, etc.Also, such wave plates may be used to convert plane polarized light tocircularly polarize light or vice versa, depending on the nature of theoptical coupling occurring in the various components and optical pathsand/or the switch 11 used in the invention.

Referring to FIGS. 5A, 5B and 5C, operation of the EDS 1 according tothe invention is depicted for use in the exemplary systems 3, 13, etc.,which are expressly described herein, and in other display systems, too.Light 4, for example, from a CRT, is horizontally polarized by thepolarizer 12. Arrow 50 represents such horizontal polarization, as doesthe dot in that arrow 50. The switch 11 is a birefringent liquid crystalcell of the type disclosed in the above-mentioned patents (such typessometimes being referred to as “surface mode” or “pi-cell” liquidcrystal devices). When the switch 11 is in the high voltage state itdoes not affect the state of polarization of the light 50. Therefore,light 51 exiting the switch 11 also has horizontal polarization, e.g.,into and out of the plane of the paper of the drawing. The light 51enters the double refracting material (birefringent material) 10 and istransmitted without any deflection and is provided as output light 52 atthe location and in the direction of arrow 5 a.

Referring to FIG. 5B, when the switch 11 is in the low voltage state, itrotates the plane of polarization of the light 50 preferably 90 degrees,i.e., into the vertical plane, as is shown by the vertical arrow 53associated with the light 51. The vertically polarized light enters thedouble refracting material 10 and its path is physically displaced, asis represented by dashed line 54 resulting in output light 52 at thelocation and in the direction of the arrow 5 b.

Briefly referring to FIG. 5C, the electro-optical dithering system 1 isshown having the light output 52 selectively switched between thelocation of the arrows 5 a when the switch 11 is in the high voltage (norotation of plane of polarization) state and the location of the arrow 5b, which occurs when the switch 11 is in the low voltage (polarizationrotating) state. The light represented by arrow 5 a is horizontallypolarized, and the light represented by the arrow 5 b is verticallypolarized, as is represented in the drawing of FIG. 5C. By selectivelyenergizing and de-energizing or, in any event, operating the switch 11between two mentioned voltage states, which switch the polarizationcharacteristic of the light, the location of the output optical signal52 can be switched between the locations represented by arrows 5 a and 5b.

A modified optical display system 60 is shown in FIG. 6 using anelectro-optical dithering system 1, as was described above, incombination with an output polarizer (analyzer) 12′. The analyzer 12′may be a linear (plane) polarizer or some other device which candiscriminate between the characteristics of light incident therein, suchas the direction of plane of polarization, circular polarization, etc.The parts of the electro-optical dithering system 1 include abirefringent material 10, such as a calcite material described above,and a switch 11, such as one of the liquid crystal cell devicesdescribed above, or some other device, as will be appreciated.

The incident light 4 is received from a light source or image source,such as a CRT 2 or some other device that delivers unpolarized lightoutput. Such unpolarized light 4 incident on the birefringent material10 is divided into two components 61, 62. The light component 61 ishorizontally polarized and it is transmitted directly through thebirefringent material 10 without deflection or refraction. The lightcomponent 62 is polarized in the vertical direction, and it is refractedso that its direction is changed (path is deflected) in the manner shownrepresentatively in FIG. 6.

It will be appreciated that here and elsewhere in this descriptionreference to directions is meant to be relative and exemplary; forexample, horizontal and vertical are meant to indicate orthogonalrelationship. Directions are exemplary and are used to facilitatedescription and understanding of the invention.

The horizontally polarized light component 61 and the verticallypolarized light component 62, the directions of polarization beingrepresented by the dots 63 and the arrow 64, respectively, are incidenton the switch 11. From the switch 11 the light components 61, 62 areincident on the analyzer 12′. That light component which has apolarization direction that is parallel to the transmission axis of theanalyzer 12′ will be transmitted through the analyzer, and the otherlight component will be blocked. Depending on whether the switch 11 isin the operative state to transmit light without rotation of the planeof polarization or is in the operative mode to rotate the plane ofpolarization of the light transmitted there through, one or the other ofthe light components 61, 62 will be transmitted through the analyzer 12′at a respective location represented by one of the arrows 5 a, 5 b.

An exemplary use of the invention is illustrated in FIG. 7 for the CRTdisplay 2 or for a liquid crystal display 20, for example. The display2, 20 has a resolution of some fixed number of raster lines or rows ofpixels that are updated periodically, for example, 60 times per second.

Assume that the speed of the display is increased, for example, isdoubled to 120 times per second to re-scan the raster lines and/or therows of pixels. The switch 11 can be synchronized with the switching ofthe display (CRT 2 or liquid crystal display 20) such that the rasterimages, for example, are alternately displaced and not displaced, e.g.,to locations 5 a and 5 b, respectively. Such synchronization may be withrespect to the blanking pulse or some other signal.

The amount of such shifting or displacement can be adjusted as aforesaidso that the displaced raster lines (or pixel rows) interdigitate thenon-displaced raster lines (pixel rows). The information on thedisplaced and non-displaced rasters (pixel rows) are selected to carrycomplementary information; and, therefore, the resolution of the entireimage displayed by the optical display system 3 or 13 is increased by afactor of 2. The same technique can be used to provide image coverageover the dead space between adjacent pixels in a liquid crystal display(or in a CRT, e.g., where a shadow mask blocks transmission ofelectrons) or to cover areas where conductors or other electricalconnections or components of a liquid crystal display, such as parts ofan active matrix array, are located, usually between adjacent pixels.

The display ordinarily would be refreshed or updated 60 times per secondto cover both the odd and even raster lines. However, by increasing therefresh or update rate to 120 times per second and using theelectro-optical dithering system to shift the location of the outputimage or optical signal for part of the time, essentially the odd andeven raster lines, while unshifted, can be refreshed or updated 60 timesper second and the odd and even raster lines, while shifted, can berefreshed or updated 60 times per second. The update or refresh times orrates presented here are exemplary; others may be used.

In FIG. 7, assuming the display 2 is a CRT, the front face 70 has aplurality of odd raster lines and a plurality of even raster lines.During operation of the CRT display 2, initially the odd raster linesare scanned to produce a first subframe (field). Subsequently, the evenraster lines are scanned, and a second subframe (field) is produced. Theinformation produced during the respective first and second subframes isreferred to as complementary and together complete an image (sometimesreferred to as a frame or picture) that is viewed. The time betweenproducing one subframe and the next is sufficiently fast that the eye ofan observer (viewer) integrates the respective first and second subframeimages to see one complete (composite) image. Similarly, using theprinciples of the present invention, the space between adjacent rasterlines can in effect be scanned to produce additional complementary imageinformation. Thus, for example, the odd lines can be scanned during thefirst subframe; the even lines can be scanned during the secondsubframe; the odd lines can be scanned during a third subframe butduring which the switch 11 of the electro-optical dithering system 1 isoperative to cause shifting of the image to the space between respectiveadjacent pairs of odd and even raster lines; and finally during a fourthsubframe analogous to the third, the even raster lines can be scannedwhile the electro-optical dithering system provides a shift of opticaloutput, to produce the shifted image between respective pairs of odd andeven raster lines. In this way resolution of the output image producedby the optical display system 3 is increased without having to increasethe resolution or space between relatively adjacent raster lines (scanlines) of the CRT display 2 and a similar technique can be used toincrease the effective number of the pixels, pixel rows, etc. toincrease resolution of the liquid crystal display 20.

Turning to FIGS. 8 and 9, an auto-stereoscopic display system 80 isshown using the electro-optical dithering system 1 of the invention. Theprinciples of auto-stereoscopic display are well known and will not bedescribed in detail here. However, the technique of obtaining theauto-stereoscopic display effect will be described.

In the auto-stereoscopic display 80, there is a CRT display 2, whichprovides a light output 4, which is delivered to a linear polarizer 12.The plane polarized light from the linear polarizer 12 is provided tothe electro-optical dithering system 1, which includes a surface modedevice (surface mode liquid crystal cell) switch 11 and doublerefracting material (birefringent material) 10. At the output of theelectro-optical dithering system 11 is a cylindrical lens array 81. Thecylindrical lens array includes a plurality of cylindrical lenseslocated in an appropriate arrangement or pattern, as is known, to directlight to or toward respective eyes 82, 83 of a person, or to some otherdevice able to detect or “see” the light received thereby. By providinga left eye image to the left eye 82 and a right eye image to the righteye 83, an individual viewing the auto-stereoscopic display system 80will discern a three dimensional or stereoscopic effect.

Using the electro-optical dithering system 1 of the invention incombination with a display source, such as a CRT display 2, a liquidcrystal display 20, or some other display, light beam steering can beaccomplished to obtain the left eye and right eye images. Therefore,auto-stereoscopic display systems can be provided easily and relativelyinexpensively.

In FIG. 9 the technique for obtaining beam steering forauto-stereoscopic effect is illustrated. Incident light 4, which isunpolarized, as is represented by the arrows and dots on the light isincident on the plane polarizer 12. Alternatively, plane polarized lightcan be provided from an image source or light source, such as a liquidcrystal display (and polarizer 12 may be eliminated). In any event, thelight which exits the polarizer 12 is plane polarized, for example, in ahorizontal plane, as is illustrated in FIG. 9. Such light then entersthe switch 11 and from there the light enters and transmits through thedouble refracting material 10. Depending on whether the switch 11rotates the plane of polarization or it does not rotate the plane ofpolarization of the light transmitted there through, the doublerefracting material 10 will deflect or will not deflect the lighttransmitted there through. In the case that the switch 11 does notrotate the plane of polarization, and the above-described alignment ofthe double refracting material 10 is provided, the light will transmitdirectly through the material 10 without deflection as light ray 90.When light ray 90 is transmitted through the interface 91 between thecylindrical lens 92 of the cylindrical lens array 81 and the externalenvironment, such as air, represented at 93, the light 90 will refractin the direction of the arrow 94 toward the left eye 82 of the observer(viewer). The light 90 traveling in the direction of the arrow 94remains polarized in the so-called horizontal direction, i.e., into andout of the plane of the paper of the drawing.

However, when the switch 11 rotates the plane of polarization of lighttransmitted there through, the double refracting material 10 deflectsthe light, as was described above, resulting in the light 95, whichtravels to a different location of the interface 91 of the lens 92. Thelight 95 refracts at the interface 91 and is bent or deflected in thedirection of the arrow 96 toward the right eye 83 of the observer. Thelight 95 is vertically polarized, i.e., the plane of polarization isparallel with the plane of the paper of the drawing of FIG. 9.

In operation of the auto-stereoscopic display 80, left eye and right eyeimages sequentially are produced by the display 2 (20) for example. Whenthe left eye image is displayed, the switch 11 does not rotate the planeof polarization, and the light 90 follows the direction of the arrow 94to the left eye 82 of the observer. When the right eye image is producedby the display, the switch 11 does rotate the plane of polarization sothat the material 10 deflects the light as light 95 which is refractedto the direction of the arrow 96 to the right eye 83 of the observer.For convenience of this description, it is understood that the indicesof refraction of the material 10 and the material of which the lens 92is made would be the same or about the same to avoid further refractionat the interface there between; however, if there is refraction there,such refraction can be taken into account, as will be appreciated bythose having ordinary skill in the art.

Referring to FIGS. 10 and 11, a display system 99, which includes aliquid crystal display 100, is shown in top plan and top section views.The display system 99 is similar to the several other display systemsdescribed herein, such as those designated 3, 13, etc. The LCD 100 has aplurality of pixels 101 arranged in respective rows 102 with dead space103 between respective rows and also at the edge 104 of the display 100.As is seen in FIG. 11, the liquid crystal display 100 includes asubstrate 105 on which an active matrix array 106 is located. The liquidcrystal display also includes a further substrate 107, a space 108between substrates where liquid crystal material 109 is located, a seal110 to close the space between the substrates, and (not shown)appropriate driving circuitry, as is well known. Light 120 representedby respective arrows illustrated in FIG. 11 is provided by a lightsource 121 and is selectively transmitted or not through the liquidcrystal display. The light 120 is plane polarized by a plane polarizer122 located between the light source 121 and the liquid crystal display100, and the light 120 is transmitted or is not transmitted as afunction of the plane of polarization thereof relative to an analyzer123, as is well known. An electrode 124 on the substrate 107 andrespective transistors and electrodes of the active matrix array 106 onthe substrate 105 apply or do not apply electric field to liquid crystalmaterial 109 at respective pixels 101 to determine whether or not theplane of polarization of light 120 is rotated and, thus, whether suchlight will be transmitted or will not be transmitted through theanalyzer 123.

The light 120 which is transmitted through the analyzer 123 is incidenton the electro-optical dithering system (EDS) 1. The electro-opticaldithering system may be operated to not shift or to shift the locationof the light 120 to locations 5 a, 5 b in the manner described above. Ifthe optical signal at locations 5 a, 5 b is complementary, as wasdescribed above, the resolution of the optical display system 99 shownin FIG. 11 can be increased. Moreover, as part of such increasedresolution, the dead space 103 where transistors 131 and/or othercomponents that are not light transmissive in the active matrix array106 effectively are covered over by the shifted light 5 b, for example.Therefore, using the electro-optical dithering system 1 in a displaysystem 99 as described, the light blocking portions of the active matrixarray, of conductors, etc., can be in effect overcome or negated whilethe overall resolution of the display is improved.

The parts shown in FIGS. 10 and 11 are in a relatively horizontalrelation showing dithering in a vertical direction. It will beappreciated that dithering can alternatively be in a horizontaldirection or, if desired, multiple electro-optical dithering systems 1can be used in optical series in order to obtain both vertical ditheringand horizontal dithering.

The LCD 100 preferably is relatively fast acting to turn on and off.Therefore, using the combination of the fast acting LCD with the EDS 1the respective lines of one subframe of information can be displayed bythe respective rows of pixels of the LCD and subsequently the interlacedlines of the next subframe can be displayed by the same respective rowsof pixels of the LCD.

The light source for the LCD 100 may be a pulsed source, which produceslight output in pulses or sequential bursts. In such case, it isdesirable to synchronize the light pulses or bursts of the light sourcewith the LCD and/or with the EDS 1. Therefore, the respective pixels ofthe LCD would transmit or block light when the light source is producinga desired light output. The amount of time that the light source istransitioning between a light transmitting or light blocking state maybe reduced and preferably is minimized. Also, the LCD would be operativeto transmit or to block light when the light source is producing itsintended light output rather than when the light source is not producinga burst of light or a desired light output. This tends to increase thecontrast of the output image, since the shutter element (LCD 100) is notchanging state when the light is pulsed, e.g. is changing its state fromlight producing to not producing or vice versa.

The EDS 1 and the LCD 100 preferably are synchronized. Therefore, whenthe LCD is producing scan lines of information from one subframe the EDSis in one state, and when the LCD is producing scan lines of informationfrom the other subframe, the EDS is in its other state thereby causingthe lines of one subframe to be interlaced with the lines of the othersubframe. The EDS and a pulsating type light source also may besynchronized so that the EDS switches states during the time that nolight output or non-optimal light output is produced by the lightsource. This further enhances contrast of the display system 3, 13, 99.

Various circuitry may be used to obtain the aforementionedsynchronization. Two examples are shown, respectively, in FIGS. 12 and13. In FIG. 12 an exemplary display system 140 is shown. In the displaysystem 140 a blanking pulse from a source 141 is supplied to respectiveLCD buffer and EDS buffer circuits 142, 143 to synchronize operation ofthem. The actual information signals from line 144 indicating the lighttransmitting or blocking state, for example, of the pixels of the LCD100, for example, as is shown in FIGS. 10 and 11, are provided the LCDbuffer 142. Those information signals are not delivered to the LCD 100,though, until appropriately coordinated or synchronized with theblanking pulses. The EDS 1 is connected to the EDS buffer 143 andreceives its drive signal from line 145 to dither or not the opticaloutput from the LCD 100. The EDS buffer also receives the blanking pulsefrom the source 141 to synchronize delivery of the signals to the EDSwith such blanking pulses and/or with the operation of the LCD bufferand information signals delivered to the LCD. The buffers 142, 143 canbe synchronized with respect to each other by appropriate timedoperation thereof with respect to the blanking pulse; or, alternatively,the buffers can be directly coupled to each other to synchronizeoperation thereof so that the dithering function is coordinated withswitching of pixels or writing of information to the LCD.

As another example of synchronization, FIG. 13 depicts a display system150 in which a pulsed light source 121, for example, receives pulsedpower from a power supply 151. A signal representing the characteristicsof the pulsed power from the powers supply 151 is provided to the LCDbuffer 142 and EDS buffer 143, which respectively receive informationand power signals on lines 144, 145 as described above. By synchronizingthe LCD 100 and EDS 1 with respect to each other and/or with respect tothe pulsing light source, the LCD can switch states as new informationis written thereto when the light source is not producing significantlight output, and/or the EDS can switch from direct transmission todithered transmission of light states when the light source is notproducing a bright output and/or the LCD is not in the process ofswitching display states.

The foregoing are but two examples of synchronization useful in thevarious display systems and embodiments of the invention. It will beappreciated by those having ordinary skill in the art that many othertypes of synchronizing techniques may be used to obtain the desiredsynchronization.

Although it may be desired to obtain full interlacing and separation ofrespective lines as in a CRT display, for example, even less than fullinterlacing, e.g., an amount of displacement that does not fullyseparate the lines but nevertheless reduces the amount of overlapthereof, will tend to reduce the above-mentioned jitter and improve theoptical output of the LCD.

Interlacing or dithering can be used to effect vertical displacement(changing of location of the optical output signal), horizontal(lateral) displacement, and/or diagonal displacement of the opticalsignal, such as that produced as the output from a pixel of a display,e.g., a CRT, LCD, or any other type of display. The direction ofdisplacement will depend on the orientation of the various components ofthe optical system. For example, in the EDS of FIG. 1 having orientationof axes of components shown in FIGS. 4A, 4B and 4C, verticaldisplacement will occur. However, by changing the relative orientationof the axes by 45 degrees or 90 degrees, the displacement as a functionof the state of the switch 11, for example, can be changed to diagonalor horizontal.

Using the vertical displacement of optical signals by the EDS 1 incombination with a display, such as an LCD, for example, it possible ineffect to double the resolution of the display in the manner describedabove. Thus, in a sense, the EDS becomes an optical line doubler whichdoubles the number of horizontal lines of resolution of the displaysystem. However, by using both vertical and horizontal displacementfunctions in a display system, it is possible to obtain in effect up toquadruple the resolution of the display relative to operation of thedisplay absent the EDS.

Referring to FIGS. 14 and 15A-15E an EDS system 201 used with a display202, in the illustrated embodiment an LCD (although other types ofdisplays can be used), is shown as a display system 203. In FIGS. 14 and15A-15E reference numerals which designate parts that are the same orsimilar to those described above are the same as the reference numeralsthat designate such above-described parts except being increased by thevalue 200. Thus, display system 203 is similar to display systems 3, 13,99, etc. mentioned herein.

However, the EDS system 201 of display system 203 includes two EDSportions 201 v and 201 h, which respectively can be operated to obtainvertical and horizontal displacement of the optical signal transmittedthere through. Each EDS 201 v, 201 h includes, respectively, a doublerefracting material 210 v, 210 h and a switch 211 v, 211 h. For example,each double refracting material may be a calcite crystal and each switchmay be a surface mode (birefringent) liquid crystal cell. The source ofoptical signals in display system 203 is a flat panel liquid crystaldisplay 202, although other types of displays may be used. The LCD 202provides light output that is plane polarized, and, therefore, aseparate polarizer like the polarizer 12 of FIG. 1, for example, may beunnecessary in the illustrated embodiment of display system 203. It willbe appreciated that although the display system 203 uses two EDS devicesor portions, the principles of the invention may be used with more thantwo EDS portions to obtain not only horizontal and vertical displacementbut also displacement in even another direction.

The relative orientation of the axes of the respective components of thedisplay system 203 is shown in FIGS. 15A-15E. Plane (linear) polarizedlight having a horizontal plane of polarization is provided by the LCD202, as is seen in FIG. 15A. In the vertical displacement EDS 201 v, theaxis of the birefringent liquid crystal switch 211 v shown in FIG. 15Bis oriented at 45 degrees to the plane of polarization of light from thesource 203; in the illustrated embodiment, such orientation is actually−45 degrees relative to vertical, for example. The projection of theaxis of the double refracting material 210 v is vertical, as is seen inFIG. 15C. In the horizontal displacement EDS 201 h, the axis of thebirefringent liquid crystal switch 211 v is oriented at +45 degrees tothe vertical (FIG. 15D), and the projection of the axis of the doublerefracting material 210 h is horizontal (FIG. 15E). The actualalignments may be slightly different from those illustrated toaccommodate or to compensate for residual birefringence in the liquidcrystal switches and/or for other purposes. Also, if desired wave platesand/or other optical components may be included with one or more of theEDS devices 201 h, 201 v to compensate for such residual retardationand/or other factors.

The display system 203 can be operated in four different states. In onestate shown in FIG. 16A with both EDS devices 201 v, 201 h of FIG. 14not displacing light, the light from the display source 202 istransmitted without being displaced; this may occur with birefringentswitches 211 v, 211 h being in high voltage, non-polarization rotatingstate and low, polarization rotating states, respectively. In a secondstate shown in FIG. 16B with EDS device 201 v, 201 h respectively notdisplacing and displacing light, the light from the display source 202is transmitted while being horizontally, but not vertically displaced;this may occur with both birefringent switches 211 v, 211 h being inhigh voltage, non-polarization rotating state. In a third state shown inFIG. 16C with both EDS devices 201 v, 201 h displacing light, the lightfrom the display source 202 is transmitted while being displaced bothhorizontally and vertically; this may occur with both birefringentswitches 211 v, 211 h being in low voltage, polarization rotating state.In a fourth state shown in FIG. 16D with EDS device 201 v, 201 hrespectively displacing and not displacing light, the light from thedisplay source 202 is transmitted while being vertically, but nothorizontally displaced; this may occur with EDS 211 v in the lowvoltage, polarization rotating state and birefringent switch 211 h beingin high voltage, non-polarization rotating state.

In FIG. 17 is illustrated a composite of the display conditions depictedin FIGS. 16A through 16D. By using relatively fast acting LCD as thedisplay source 202 and two EDS devices 201 h, 201 v synchronized andoperated in the manner just described so that the pixels first are shownin the manner in FIG. 16A, then as in FIG. 16B, etc., sufficientlyquickly that the observer's eyes tend to integrate the respectiveimages, a high resolution image with a pixel density like that shown inFIG. 17 can be obtained. It will be appreciated that an exemplaryoptimum improvement in resolution using the display system 203 in thedescribed manner can increase resolution of the display 202 byapproximately a factor of 4.

Thus, it will be appreciated that the respective switches 211 v, 211 hmay be operated according to the following table to obtain theabove-described operation controllably to vertically shift or displaceand/or to horizontally shift or displace the optical signals from thedisplay 202. High means electrically operated so as to be notpolarization rotating and low means electrically operated so as to bepolarization rotating, although other conventions may be used.

TABLE 1 Switch 211v Switch 211h High Low High High Low Low Low High

In the present invention the switches and double refracting material maybe substantially optically transparent. Therefore, those components donot tend to absorb light. The use of such components in a display system203, for example, does not ordinarily significantly reduce thebrightness of the display output. Although two or more images are placedsequentially in the field of view provided by the display system 3, 13,99, 203, etc., brightness of the display output is not diminished;rather, image resolution can be increased.

Other types of birefringent materials and/or devices may be used inplace of or in addition to the calcite material double refracting device10 described above. For example, other types of crystal materials and/orminerals may be used; the amount of displacement between an unrefractedoptical signal and a refracted optical signal by such double refractingmaterial would depend on index of refraction characteristics of thedouble refracting material, the index of refraction of the environmentexternal of the double refracting material, wavelength of opticalsignal, and distance the optical signal travels in the double refractingmaterial.

Another double refracting material which may be used in the invention ascomponent 10, for example, is liquid crystal material. Liquid crystalmaterial, such as nematic liquid crystal and smectic liquid crystalmaterial may be birefringent and may be used. Other types ofbirefringent liquid crystal materials also may be used. By organizing ororienting the liquid crystal material in a particular organization ororientation, the transmission of light-there through with or withoutrefracting the light can be dependent on the direction of electricvector of the light, e.g., the plane of polarization of plane polarizedlight.

A polymer liquid crystal may be especially useful as such a doublerefracting material, for such material both can have a relatively largebirefringence and also can be formed into a solid material whichmaintains the orientation of the structure of the liquid crystalmaterial thereof. Polymer liquid crystal materials are known.

However, if the double refracting material were of a liquid crystalmaterial whose structural orientation or organization could be switched,e.g., in response to application of a prescribed input such as anelectric field (or removal of such field or changing voltage or someother characteristic of the field, etc.), then the function of the twocomponents of an EDS may be replaced by a single switchable liquidcrystal shutter type device. In this case the liquid crystal shuttercould provide one index of refraction or birefringence characteristic torefract light transmitted there through a given amount and a differentindex of refraction characteristic with no birefringence so as not torefract such light or with parameters to refract the light a differentamount.

An embodiment of display system 203′ which uses a pair of switchableliquid crystal cells 270, 271 associated with a liquid crystal display202′ is shown in FIGS. 18 and 19. Each of the liquid crystal cells 270,271 functions as a combination of birefringent or double refractingmaterial 210 h, 210 v and as a switch 211 h, 211 v. The liquid crystalcells may be, for example, aligned like a birefringent liquid crystalcell using nematic or smectic liquid crystal material between a pair ofglass plates. The plates are treated so the liquid crystal is alignedgenerally in the same direction at both plates without twisting; and,therefore is so aligned throughout the cell. The liquid crystal materialpreferably is tilted, e.g., at 45 degrees, to obtain a desiredbirefringence characteristic; but although tilted, the projection of theaxis of the liquid crystal structure would be in the same plane as theplane of polarization of incident light thereon to obtain the desiredbirefringence characteristic. The exemplary arrangement of axes of thedisplay system 203′ is shown in FIG. 19.

By changing the electrical drive signal to the respective liquid crystalcells 270, 271, the index of refraction characteristics thereof can bechanged, and, as a result, the location of the optical signaltransmitted there through can be changed, e.g., dithered as describedherein. For example, for plane polarized light incident on liquidcrystal cell 270 which has liquid crystal therein structurally alignedsuch that the light experiences the ordinary index of refraction of theliquid crystal and no birefringence, the light will transmit directlythrough the liquid crystal cell without refraction. However, if theliquid crystal is structurally aligned such that the light experiencesthe extraordinary index of refraction and, thus, birefringence, thelight will be refracted at the interface between the liquid crystalmaterial and the glass plate or the like forming or at one surface ofthe liquid crystal cell 270 at one side; and the light will be refractedagain at the interface between the liquid crystal and the glass plateetc. at the other surface of the liquid crystal cell so as to beparallel with the light incident on the liquid crystal cell 270 butdisplaced from the extension of the transmission axis of the incidentlight.

Thus, by selectively operating, e.g., energizing and deenergizing orchanging energization level, the liquid crystal cells 270, 271, then,can change the location of the optical signal output by the displaysystem 203′. The liquid crystal should be aligned to present to thelight transmitted there through either the ordinary or extraordinaryaxis or index of refraction and appropriate birefringence characteristicas described above. If only one liquid crystal cell 270 is used, theoptical signal can be changed back and forth in one plane or direction.If two liquid crystal cells 270, 271 (like the cell 270, for example)are used and are arranged such that the axes thereof are non parallel,then the optical signal can be changed back and forth in two planes ordirections. Such non-parallel alignment may be perpendicular alignmentto obtain up/down dithering and left/right dithering relationships.Since the plane of polarization of light incident on the liquid crystalcell 271 should be parallel to the axis of that cell, a half wave plate272 may be placed between the liquid crystal cells 270, 271 to rotatethe plane of polarization of the light exiting the liquid crystal cell270. For example, the axis of such half wave plate may be oriented at 45degrees relative to the plane of polarization, i.e., half way betweenthe 90 degrees desired rotation. It is noted that a polarizer 12 isshown in FIGS. 18 and 19; such polarizer helps assure the quality ofpolarization of the light from the display; but such polarizer can beeliminated if the output from the display is of sufficient quality ofpolarization, e.g., minimal amount of unpolarized light includedtherein.

The EDS 1, 201 may be used in a display system 3, 13, 99, 203, 203′,etc. which is monochrome or multicolor. Operation for a monochromedisplay system would be, for example, as is described above. Oneembodiment exemplifying operation for a multicolor, such as a red, greenand blue (rgb), display system can employ the above-described type ofoperation for each color. Therefore, when one color or a group of colorsis being displayed by respective pixels of such a color display, theoptical signal output can be either transmitted without displacement orwith displacement in the manner described above. As is depictedschematically in FIG. 20, part of a display 202′, e.g., similar todisplay 202, is shown including three representative adjacent pixeltriads 281, 282, 283, each including a red, green and blue pixelportion. The display 202′ may be operated in a color frame sequentialmode in which respective red, green and blue frames or images areproduced in time sequence. In this case all red pixels of respectivepixel triads 281, 282, 283, etc. would be red where it is desired in thefinal image to have red light; subsequently green and then blue pixelsof the image would be created. Alternatively, the respective red, greenand blue pixels of respective triads can be displaying respective colorssimultaneously. In either case, the principles of the invention usingthe EDS 1, 101, etc. may be used to increase resolution of the outputimage in the above-described manner.

However, the EDS may be used for the purpose of selectively dithering(displacing) less than all of the color frames of a multicolor display,especially if the display is operated in a color frame sequential mode.For example, the dithering function can be used selectively to displaceor not the green optical signal (light produced during the green frame)of the display 3, 13, 99, 203, 200′; however, the EDS may be used so itdoes not selectively to dither the optical signal during one or both ofthe other color frames. Since the human eye is more sensitive to greenlight than to red or blue light, a significant enhancement of theapparent resolution of the multicolor display can be achieved by onlyselectively dithering the green light optical signal. If desired, thegreen and red optical signals can be selectively dithered withoutselectively dithering the blue optical signal; and this will result inan even greater apparent resolution of the multicolor display than ifonly the green optical signal were selectively dithered. Since the humaneye is not as sensitive to blue light as it is to red or green light,the fact that resolution of the blue light or blue frame component ofthe overall image is not enhanced by the dithering of the invention maynot significantly reduce the resolution of the composite multicoloroutput image. By reducing the amount of dithering required, it ispossible that the complexity and/or cost of the electronic drive andtiming circuitry employed in the invention can be reduced.

Referring to FIGS. 21, and 22A-22F, there is shown a schematicillustration depicting a time sequence of operation of the inventionusing a segmented display system 403. FIG. 22A represents the outputoperation of the display system 403 at one period of time; FIG. 22Brepresents operation at the next period of time; and so on. In FIGS. 21and 22A-22F the various parts which correspond to parts described aboveare identified by the same reference numerals but increased to a 400series. Thus, display system 3, 13, 99, 203, 203′, etc. in FIGS. 21 and22A-22F is designated 403, for example.

The face 470 of the display system 403 in FIGS. 21 and 22A-22F isdivided into three separate segments 470 a, 470 b, 470 c. Morespecifically, the display 402 may include a CRT or an LCD 2, 20, 102,etc., and between the display and the viewer, for example, is at leastone, and possibly several in series, electro-optical dithering system 1,11, 21, 101, as was described in the several embodiments above. Forsimplicity of description here the display system 403 is described withonly one EDS, though.

The EDS 401 includes, for example, a double refracting material 410 anda switch 411 such as a surface mode liquid crystal cell. However, theswitch 411 is segmented into several areas which can be separatelyaddressed to change the optical characteristics thereof. The switch 411is shown in FIGS. 21 and 22A-22F as having three separate segments 411a, 411 b, 411 c; but it will be appreciated that the switch may havefewer or more segments. Each segment 411 a, 411 b, 411 c can beseparately operated to change or not to change the direction of plane ofpolarization of light transmitted there through. Each segment can be aseparate liquid crystal cell or each can be part of the same liquidcrystal cell which has an electrode arrangement which permits operatingof the different parts separately.

In FIGS. 22A, 22B, 22C, respectively, (with reference also to FIG. 21)the first subframe (field) of information is written sequentially to theupper, middle and lower thirds 402 a, 402 b, 402 c of the display 402for direct transmission without being dithered or shifted in position.By the time the information is being written to the middle third of thedisplay 402, the information written to the top third begins fading; andby the time the information is being written to the bottom third, theinformation at the top third is substantially fully faded and that atthe middle third is beginning to fade.

In FIG. 22D the start of information representing the second subframe(field) being written to the display 402, initially to the top third 402a of the display, is shown. The dithered information optical signal inthe top third of FIG. 22D is represented by the illustrated dashedlines. Since such information is for the second subframe, the opticalsignal output is intended to be dithered/changed; however, at this timethe image or optical output presented by the middle third 402 b of thedisplay 402 has not completely faded. Therefore, if the optical outputof the entire display 402 were dithered at this time, the opticalinformation or optical output signal still being displayed at the middlethird would be shifted to an incorrect location. To avoid this wrongfulshifting of the optical signal from the middle third at this time, onlythe top third 402 a of the display 402 is dithered. Preferably the topthird actually is dithered when the previous image there has faded; andthat actually can occur at the time period represented in FIG. 22C.

At the time period represented by FIG. 22D the middle third of thedisplay 402 has faded, and is dithered; and at the time periodrepresented by FIG. 22E, information is written to that dithered middlethird of the display, and the bottom third which has faded is dithered.At the time period represented by FIG. 22F, the dithered imageinformation is written to the bottom third of the display 402 and thetop third is dithered since the information previously written there bynow has faded.

The above-described operation of the display system 403 can continuesequentially as the respective subframes are sequentially displayed,e.g., the optical signals comprising such subframes are presented as theoutput of the display system. In each subframe the different respectiveparts or segments are sequentially dithered or not preferably so that asegment is already undithered or dithered before the raster, line, row,etc. of information to form the optical signal is written to therespective pixels of that segment. The dithering or unditheringswitching action, e.g., operation of the respective switches 411 a, 411b, 411 c from one state to the other, also can be carried out as theaction of writing information to a segment is carried out; butordinarily it would be better to effect the dithering or unditheringwhen the segment is relatively blank (e.g., information there has faded)to avoid undertaking a dithering or undithering action while an opticaloutput is being displayed.

It will be appreciated that the segmentation technique may be used withdisplay system which uses a CRT display, a liquid crystal display orsome other type of display. The segmented switch 411 approach also isuseful to remove artifacts caused by a relatively slow acting LCD.

Further, it will be appreciated that the various EDS embodiments of thepresent invention and display systems using such EDS embodiments areoperative to move, shift, translate, etc. an output optical signal fromone location to another without substantially affecting brightness ofthe display system or optical signal. The components of the EDSgenerally are optically transparent, and, therefore, other than arelatively minor amount of absorption of light transmitted therethrough, there may be otherwise relatively little reduction in lightintensity. Therefore, the features of the invention may be used for thevarious purposes described herein, for example, to increase resolution,to cover or to reduce the effective optical dead space, etc., withoutreducing brightness of the optical output.

A passive dithering system 500 in accordance with one aspect of thepresent invention is illustrated schematically in FIG. 23 in an opticaldisplay system 501. The passive dithering system 500 as shown is used inconnection with a display 502 which produces an output of polarizedlight, such as might be produced by a twisted nematic (TN) based flatpanel liquid crystal display 504 incorporating a linear polarizer 506 orby a CRT display with an added linear polarizer interposed, as is thepolarizer 506, between the CRT display and the dithering system 500. Thedithering system 500 includes a pair of double refracting orbirefringent material layers 508 h, 508 v, such as a calcite crystalmaterial, separated by a half wave plate 510. A wave plate 512, such asa quarter wave plate, turns plane polarized light into circularlypolarized light; circularly polarized light can mathematically beresolved into equal amplitudes of vertical and horizontal planepolarization separated in phase by 90□. Thus, the quarter wave plate ina sense separates incident plane polarized light into relativelyorthogonal plane polarized components for delivery to the birefringentmaterial 508 h as an input for the dithering system 500. The effect ofthe passive dithering system 500 can be to enhance the resolution of thedisplay output by reducing fixed pattern noise in the display. Thepassive dithering system 500 can increase the number of output pixelsprovided simultaneously by an optical display system.

In FIG. 24 a a very generalized example of the function of the passivedithering system 500 is shown considering an image 520 a created by asingle pixel 520 of the flat panel liquid crystal display 504 separatedfrom adjacent pixels 522 in the display by optical dead space 524. Thebirefringent material 508 h effectively creates a double image 520 b ofthe image 520 a which is displaced or dithered in, for example, ahorizontal direction, as is shown in FIG. 24 b. The second birefringentmaterial 508 v, which receives both images 520 a and 520 b, creates asecond pair of images 520 c, 520 d displaced vertically from the firstpair of images as is shown in FIG. 24 c. In this way, the image producedby a single pixel, such as exemplary pixel 520, can be made to fill orat least to increase the fill of the optical dead space 524 between thepixels 522 which is typically used to electrically isolate adjacentpixels and to accommodate circuitry and electrical components. In otherwords, the dithering system 500 increases the fill factor of the display502 as viewed. Therefore, the passive dithering system 500 expands orenlarges the respective pixels. In the example of FIGS. 24 a, 24 b, 24c, the pixel 520 a can be said to have been expanded or enlarged tocover the area shown in FIG. 24 c being occupied by images 520 a, b, c,d.

If desired, the locations at which the passively dithered or createdimages 520 b, c, d are placed may be other than or in addition to theoptical dead space 524. For example, such image may be placed to overlapanother image or pixel, to overlap several images or pixels, image(s)and optical dead space, etc., for example, as is described furtherbelow.

One possible manner of orienting the axes of the optical components ofthe passive dithering system 500 in the optical display system 501 isshown in FIG. 25 a. The linear polarizer 506 or polarized display outputis oriented vertically so that an image of a pixel emerging from thepolarizer or display will be linearly polarized in a vertical direction,as is shown at pixel 520 a in FIG. 25 b. In FIGS. 25 b-g the respectivearrows represent direction or plane of polarization of light. Thequarter wave plate 512 is aligned with its axis 512′ at 45□ to the planeof polarization of the plane (linearly) polarized light incidentthereon, e.g., from the polarizer 506. With this arrangement the quarterwave plate 512 converts the incident plane polarized light to circularlypolarized light. Circularly polarized light in effect can be resolvedinto two orthogonal plane polarized components 520 a′, 520 a″ which areout of phase by 90□, and such resolution is shown for pixel 520 a inFIG. 25 c. The birefringent material 508 h is arranged relative to thelinear polarizer 506 and quarter wave plate 512 with the projection ofits optic axis 508 h′ into the plane of the polarizer 506 and quarterwave plate 512 being horizontal, e.g., parallel to the polarized lightcomponent 520 a″ and perpendicular to the polarized light component 520a′. The axis 510′ of the half wave plate 510 is oriented at +22.5degrees to vertical, and the second birefringent material 508 v isoriented with the projection of its optic axis 508 v′ into the plane ofthe polarizer 506, etc. being vertical. It will be appreciated, however,that this arrangement is only one of many possible arrangements of theaxes of the components which would produce the dithering or pixelexpanding or enlarging effect described herein and/or similar orequivalent effects.

With further reference to FIGS. 25 a-g, which additionally illustratesthe path of an image through the passive dithering system 500, the pathof the exemplary pixel image 520 a through the system will be describedin greater detail. As oriented, the linear polarizer 506 transmitsoptical information in the form of pixel images from pixels in thedisplay which have effected the light transmitted there through so as tobe polarized in the direction of the transmissive axis 506′ of thelinear polarizer. For the exemplary image 520 a in FIG. 25 b, the lightwould thus be polarized in a vertical direction represented by arrow 520a′.

Since the plane of polarization of the image 520 a is at a 45 degreeangle to the optic axis 512′ of the quarter wave plate 512, the quarterwave plate converts the plane polarized incident light to circularlypolarized light. The circularly polarized light can be resolved orconsidered as two plane polarized light components 520 a′, 520 a″ (FIG.25 c) the planes of polarization of which are orthogonal and the phasesof which are 90□ out of phase. It will be appreciated that other meansor techniques may be used to divide the plane polarized light, which isdelivered to the birefringent material 508 h, into plural componentswhich are acted on differently by the birefringent material, for exampleacted on in the manner illustrated in FIGS. 25 a-g or in some othermanner.

Since the plane of polarization 520 a″ of some of the light representingpixel 520 a in FIG. 25 c, which is incident on the birefringent material508 h, is in the place of the optic axis 508 h′ and encountersbirefringence due to the tilting of the optic axis 508 h′ as wasdescribed above, e.g., with respect to FIGS. 1-6, such light isrefracted by the birefringent material to form the pixel 520 b at alocation displaced, for example, to the right from pixel 520 a, as isseen in FIG. 25 d. Also, since the plane of polarization 520 a′ of someof the light representing pixel 520 a in FIG. 25 c, which is incident onthe birefringent material, 508 h, is perpendicular to the optic axis 508h′, the path of such light is not altered by the birefringent material,and pixel 520 a is located as is shown in FIG. 25 d. Summarizing, as theorthogonally related polarized components pass through the birefringentmaterial 508 h, one of the polarized components will be refracted anddeflected horizontally while the other component will be unaffected. Asa result, the birefringent material 508 h will yield two images, animage 520 a in its original location and a horizontally displaced image520 b with the images being polarized orthogonally to one another.

The images 520 a and 520 b then pass through the next optical componentin the passive dithering system 500, the half wave plate 510, where theplane of polarization of each of the images 520 a and 520 b iseffectively rotated +45 degrees so that the plane of polarization ofeach image is as shown in FIG. 25 e. The polarizations represented byarrows 520 a′″ and 520 b″ for pixel images 520 a, 520 b in FIG. 25 e arethe vector equivalents to the polarizations represented by therespective arrows 520 a′, 520 a″, 520 b′, 520 b″ for pixels 520 a, 520 bin FIG. 25 f. Two of such vector equivalent polarizations of FIG. 25 fare parallel to the optic axis 508 v′ of the second birefringentmaterial 508 v, and two are perpendicular to the optical axis 508 v′.Due to such relationships of the planes of polarization of each of theimages 520 a and 520 b in FIG. 25 f to the axis 508 v′ of thebirefringent material 508 v, the images 520 a and 520 b will be resolvedinto their orthogonally polarized components 520 c, 520 d, respectively,as these components pass through the birefringent material 508 v. Thepolarized components of each image 520 a, 520 b which are parallel (520a′, 520 b′″) to the plane containing the axis 508 v′ will be refractedand deflected vertically to result in images 520 c and 520 d while theother polarized components 520 a″, 520 b′, which are perpendicular tothe axis 508 v′ (or the plane containing that axis) will be unaffected.As a result, the original image 520 a is dithered into four images 520a, 520 b, 520 c and 520 d. These images may be of substantially equalintensity.

While the passive dithering system 500 discussed above was illustratedas doubling images in two directions, horizontal and vertical, a passivedithering system that doubles the image in only a single direction onlyis also possible. Such a system may include a single birefringentmaterial used in conjunction with a display producing a polarized ornon-polarized output to result in a doubled pixel image or to performpassive line doubling.

Also, it will be appreciated that the above description with respect toFIGS. 23, 24 a-c, and 25 a-g is exemplary, and other arrangements ofcomponents to compose a passive dithering system to obtain a desiredpixel enlarging, expanding, shifting, etc. may be employed. For example,a birefringent liquid crystal cell may be used as a wave plate: asurface mode liquid crystal (e.g., U.S. Pat. No. Re. 32,521) cell or api-cell liquid crystal cell (e.g., U.S. Pat. No. 4,582,396) which istuned to the desired retardation of quarter wave or half wave areexamples. The birefringent material may be liquid crystal cells. Variouscrystals, prisms, or other devices may be used to provide birefringenceand/or polarizing functions. By changing the amount of birefringence andoptical path length through a birefringent material the amount ofdeflection of a pixel image can be determined. Changing relativeorientation of axis of one or more components can change the direction apixel is shifted. Of course, the illustrated alignment of components isrelative and reference to vertical, horizontal, into or out of the planeof the paper or drawing only is for convenience of description. All suchequivalent and alternate or additional materials and/or alignments ofcomponents and functional operation are considered within the scope ofthe present invention.

As is evident from the description above with respect to FIGS. 23-25 andthe description below with respect to FIGS. 26-32, in an exemplarypassive dithering system of the invention, birefringent material may beused to change location of light representing a pixel, an image of apixel, or another optical signal (for convenience sometimes simplyreferred to as pixel). The passive dithering system, therefore, is ableto change the apparent location of the pixel. Such change may result inan increase in or enlarging of the pixel size, in a doubling orduplicating of the pixel, etc; such change in location may simply be achange in the apparent location of the pixel without any doubling,duplicating, changing of size, etc.

When the passive dithering system is used to dither a pixel to changesize, e.g., effectively to enlarge the pixel, the dithering system maycause there to be multiple spaced apart pixels derived from the originalpixel or pixels. Alternatively, one or more of the multiple pixels mayoverlap or be sufficiently adjacent to another pixel as to be consideredtouching or in any event not spaced apart. As an example, by enlarging apixel to cover optical dead space of a display, the apparent resolutionof the display usually is increased even without increasing the actualnumber of pixels driven by the display.

In the case of a pixel being expanded using an exemplary passivedithering system according to the invention, light from the originalpixel is distributed over a viewed area that is larger than the area ofthe original pixel of the display. However, the total amount of lightreaching the eye of an observer, for example, remains substantially thesame as that provided by the original pixel before being expandedbecause the components of the passive dithering system are not the lightabsorbing or blocking type. Therefore, the apparent brightness of adisplay when used in combination with such a passive dithering systemwould tend not to be diminished.

The passive dithering system of the invention is described with respectto several embodiments. These embodiments are examples of components andarrangements of components to obtain the passive dithering effect of theinvention. Many other components and arrangements of components also maybe used to obtain passive dithering, as will be appreciated by those whohave ordinary skill in the art.

For example, in the embodiments of passive dithering systems illustratedin FIGS. 23-27 a half wave plate is used to set up particular planepolarization conditions, such as direction of plane of polarization; andin the embodiments illustrated in FIGS. 28-32 a quarter wave plate isused to set up particular plane polarization conditions. In theembodiments of passive dithering systems illustrated in FIGS. 23-25 and28-30 the passive dithering systems receive plane polarized light inputfrom a liquid crystal display that provides plane polarized light outputor from another display which may not provide a plane polarized lightoutput but which is used in combination with a plane polarizer to obtainthe desired polarized light input to the dithering system. However, inthe embodiments illustrated in FIGS. 26, 27, 31 and 32 the passivedithering systems receive and operate on unpolarized light.

The components of the respective passive dithering systems describedwith respect to FIGS. 23-32 are arranged to expand a single pixel orlight forming that pixel to four pixels which are arranged in a two bytwo rectilinear array, such as that depicted by pixels 524 a-d in FIG.24 c. However, it will be appreciated by those who have ordinary skillin the art that the passive dithering systems of the invention may beadjusted, including changing of optical axes orientations, changing ofbirefringence value, adding or deleting components, etc., to expand thesingle pixel to fewer or to more than four pixels and to arrange thosepixels in a rectilinear array or in another pattern or arrangement.Also, although quarter wave plates and half wave plates are discloseduseful in passive dithering systems, it will be appreciated that othertypes of wave plates or appropriate means may be used, too. Preferablythe wave plates and/or other appropriate means provide the same orsubstantially the same wave plate function, such as optical retardation,for all, for a relatively wide range of wavelengths of light or at leastfor the wavelength range intended to be used.

Using the principles of the invention to expand a pixel formed of planepolarized light, the incident plane polarized light is divided into twoorthogonally related plane polarized components. A quarter wave platemay be used for this function. A quarter wave plate having its opticaxis aligned at 45□ to the plane of polarization of incident planepolarized light converts the plane polarized light to circular polarizedlight, which can be resolved to orthogonally related plane polarizedcomponents which are of equal amplitude but are out of phase by 90□. Ifthe quarter wave plate is oriented at other than 45□ to the plane of theincident plane polarized light, the output there from will beelliptically polarized, which also may be resolved to respective planepolarized components possibly with phases that differ by other than 90□and/or amplitudes which are not equivalent. Means other than a quarterwave plate also may be used to effect such separating of the incidentplane polarized light into respective distinguishable components. Theincident plane polarized light, which is resolved to respectivedistinguishable components, is directed to the birefringent material,which separates the components in effect by directing them to differentlocations and thereby expands the apparent area of the pixel.

For unpolarized light input to a passive dithering system of theinvention used, for example, to expand a pixel, the incident light isdirected to birefringent material usually without the need to planepolarize the incident light. Since the incident light already includesor can be considered as being resolved to two orthogonally related planepolarized components, the birefringent material separates the respectiveorthogonally plane polarized components in effect by directing them todifferent locations and thereby expands the apparent area of the pixel.

Referring to FIG. 26, there is shown a passive dithering system 500′ ofan optical display system 501′ used in connection with a display 532which produces non-polarized (unpolarized) light, such as a nematiccurvilinear aligned phase liquid crystal (NCAP), polymer dispersedliquid crystal (PDLC) or liquid crystal polymer composite (LCPC) basedflat panel liquid crystal display. The passive dithering system 500′ ofFIG. 26 includes the same optical components as the dithering system 500described above relative to FIG. 23-25, such as a birefringent material508 h, a wave plate 510 and a second birefringent material 508 v. Inthis instance, neither the passive dithering system 500′ nor the display532 is provided with a linear polarizer to polarize the output lightfrom the display.

In operation, the passive dithering system 500′ when used in connectionwith a display producing non-polarized light will result in horizontaland vertical pixel image doubling similar to that produced by thepassive dithering system 500 and shown in FIGS. 23-25. In fact, theorientations of the optic axes 508 h′, 510′ and 508 v′ of the components508 h, 510, 508 v, shown in FIGS. 26 and 27 may be the same as whenthose components are used in connection with a display producing apolarized output. (If it were desired to use the dithering system 500with an unpolarized light producing display 532, the polarizer 506 couldbe placed optically between the display 532 and the dithering system 500in the manner shown in FIGS. 23-25, for example).

One possible set of orientations for the optic axes of these componentsis shown in FIG. 27. The optic axis 508 v′ of the first birefringentmaterial 508 v is vertical and is tipped as was described above, theaxis 510′ of the half wave plate 510 is at +22.5□ to vertical and theprojection of the optic axis 508 h′ of the second birefringent material508 h into the plane of the page is horizontal and is tipped as wasdescribed above. Although the light which enters the first birefringentmaterial 508 v is non-polarized, it can be visualized as polarized lightresolved into two orthogonal components such as a vertical andhorizontal polarized component as shown by arrows in the exemplary pixelimage 534 a created by a corresponding pixel 534 in the display 532.

The components 508 v, 510 and 508 h then function basically as describedabove in FIG. 25. The first birefringent material 508 v will resolve theindividual components of the pixel image 534 a into their orthogonalcomponents and will dither (shift location of) one polarized componentrelative to the other polarized component to produce a verticallydisplaced double image of the pixel image 534 a. The half wave plate 510will then rotate the polarization components of those images as in FIG.25 e so they are at 45□ angles to the optic axis 508 h′ of the secondbirefringent material 508 h where the images will be doubled anddisplaced in a horizontal direction as in FIG. 25 g. As a result, theinitial image 534 a is doubled in the vertical direction and then theinitial image and the doubled image are doubled in the horizontaldirection to produce four adjacent images which may substantially coverthe portion of the original pixel 534 a in the display and dead spacesurrounding the pixel in one vertical and horizontal direction.

FIG. 28 illustrates an alternate embodiment of a passive ditheringsystem 540 of an optical display system 541 shown with an opticaldisplay which produces linearly polarized output light, such as by atwisted nematic based flat panel liquid crystal display 542incorporating a linear polarizer 544. The passive dithering system 540includes a first birefringent material 546 v, a second birefringentmaterial 546 h and quarter wave plates 548, 549, respectively,interposed between the source of polarized light (display 542 and, ifused, polarizer 544) and the first birefringent material 546 v andbetween the birefringent materials 546 h and 546 v. One possible set oforientations for the axes of the linear polarizer 544 of the display,the birefringent materials 546 v and 546 h and the quarter wave plates548, 549 is shown in FIG. 29. The linear polarizer 544 has atransmissive axis in the vertical direction. The projection of the opticaxis of the first birefringent material 546 h into the plane of thetransmission axis of the linear polarizer also is vertical, i.e.,parallel to the axis of the polarizer. The axes of the quarter waveplates 548, 549 are oriented +45□ to vertical and the projection of theoptic axis of the second birefringent material 546 h into the plane ofthe linear polarizer is at +90□ to vertical, i.e., horizontal.

The passive dithering system 540 functions basically the same way as thepassive dithering system 500 is described above relative to FIG. 25. Thefunction of the half wave plate 510 in the passive dithering system 500has been replaced in the system 540 by a quarter wave plate 549. Thequarter wave plate 548 and birefringent material 546 v function as thequarter wave plate 512 and birefringent material 508 h of FIGS. 23-25.The quarter wave plate 549 effectively divides the polarized lightcomponents of light passing through the wave plate 549 by converting thelight to circularly polarized light and its respective equivalentorthogonal plane polarized components like the quarter wave plates 512,548 do. The components of the circularly polarized light are thendithered by the second birefringent material 546 h in a horizontaldirection as explained above for the passive dithering system 500. Oneadvantage of using the quarter wave plate 549 as opposed to the halfwave plate 510 or 510′ is that the quarter wave plate 549 will tend tointroduce less chromatic aberration on the light passing there throughsince a quarter wave plate usually is thinner material than a half waveplate and, therefore, usually is less dispersive, e.g., exhibits lessoptical dispersion.

In FIGS. 30 a-30 e are shown the operation of the passive ditheringsystem 540 of FIGS. 28 and 29. In FIG. 30 a a pixel 542 a of display 542is shown. Light from pixel 542 a is vertically polarized and isrepresented by the vertical arrow therein. The linear polarization isproduced by the display 542 and/or is due to the polarizer 544. Aseparate polarizer 544 ordinarily is unnecessary if the display 542produces polarized light output. Optical dead space 550 surrounds thepixel 542 a.

The quarter wave plate 548 divides the vertically polarized light fromthe polarizer 544 to obtain two orthogonal plane polarized components,as is seen in FIG. 30 b. In FIG. 30 c it can be seen that thebirefringent material 546 v changes the location of the verticallypolarized light component portion of light incident thereon moving thatlight vertically relative to the location of the vertically polarizedlight component portion. Therefore, pixel 542 a is expanded, e.g., isdoubled, in that pixel area 542 b now has been created. The quarter waveplate 549 divides (resolves) the plane polarized light from thebirefringent material 546 v so that each pixel 542 a, 542 b has bothorthogonal plane polarized light components, e.g., horizontal andvertical, as is shown in FIG. 30 d. In the manner described above, thedouble refracting material 546 h expands, e.g., doubles, the pixels 542a, 542 b to create pixel areas 542 a, 542 b, 542 c, 542 d shown in FIG.30 e.

FIGS. 31 and 32 illustrate a passive dithering system 540′ which isidentical to the passive dithering system 540 shown in FIGS. 28-30 butit is used in an optical display system 541′ with a display producingnon-polarized (unpolarized) output light, such as an NCAP, PDLC or LCPCbased flat panel liquid crystal display 560 e.g., like the display 532and pixels 534 of FIGS. 26 and 27. The orientation of the birefringentmaterials 546 v and 546 h and the quarter wave plate 549, which arerepresented in FIG. 32, may be the same as those described for the likecomponents for the passive dithering system 540 although it would beappreciated that this is only one possible set of orientations for theaxes of the components which would dither an image in the mannerdescribed above. The passive dithering system 540′ functions inbasically the same way described above for the system 540 but onunpolarized input light, which is resolved as orthogonally related planepolarized light components (see the description above concerning FIGS.26 and 27), as opposed to the linearly polarized light which the system540 receives from the display 542.

It also will be appreciated that the several features and embodiments ofthe invention illustrated and/or described herein may be used with otherfeatures and embodiments that are illustrated and/or described herein aswell as equivalents thereof. For example, in the segmented displaysystem described the EDS may be formed by a calcite crystal and asurface mode liquid crystal cell, by a calcite crystal and a twistednematic liquid crystal cell or by some other type of switch and/or someother type of double refracting material. Also, the EDS may be a liquidcrystal EDS in which both the switch function and the double refractingfunction can be carried out by the same device, e.g., as in theembodiment of FIGS. 18 and 19. Moreover, in many instances passivedithering systems may be used in conjunction with or as a substitute forsome of all of the components described for the EDS. These are simplyexamples of combining features and it will be appreciated that othercombinations also may be made consistent with the spirit and scope ofthe invention.

From the foregoing it will be appreciated that various embodiments ofthe invention using principles described herein may be employed withpolarized light or unpolarized light. If it possible to operate based onan unpolarized light as an input to the dithering system, e.g., using anNCAP display, there is no need for a polarizer and the undesirableeffect that a polarizer has in blocking approximately 50% of thetransmitted light. It also will be appreciated that in variousembodiments described herein a quarter wave plate may be used, a halfwave plate may be used, and/or a combination thereof may be used. Invarious embodiments a half wave plate may be substituted for one or morequarter wave plates and vice versa. A quarter wave plate may be used toconvert plane polarized light to circular polarized light or toorthogonal components of plane polarized light. A quarter wave platealso may be used to convert plane polarized light to ellipticallypolarized light. A half wave plate is used to rotate the plane ofpolarization of plane polarized light. Usually the half wave plate willrotate the plane of polarization by twice the angle between the plane ofincident plane polarized light and the axis of the half wave plate.

Turning to FIG. 33 an active dithering system 601 is used with a display602 in an optical display system 603. The dithering system includes abirefringent material 610, such as a calcite crystal, having an axis610′ that is oriented at an angle theta relative to horizontal, as isdepicted in FIG. 33. The dithering system 601 also includes a switch611, such as a birefringent liquid crystal cell of the type describedabove. The display 602 may be a liquid crystal display that providesplane polarized light output that has a vertical plane of polarizationrepresented by the arrow 602′. Alternatively, the display 602 mayprovide other than plane polarized light output, and in that case aplane polarizer 612 may be used to provide such vertical polarization ofthe light delivered from the display and polarizer to the switch 611.The orientation of the axis of the birefringent liquid crystal switch611 is at 45 □ to the vertical plane of polarization 602′, as isrepresented by the arrow 611′. As was described, as the switch 611 isenergized or not, the plane of polarization of the light output therefrom will be the same as the direction of the arrow 602′ or not, i.e.,vertical, or horizontal. A half wave plate 615 between the switch 611and the birefringent material 610 has its axis 615′ oriented at an anglerelative to horizontal that is ½ theta.

With reference to FIGS. 33 and 34, which presents representativeoperation of the dithering system 601, when the light transmittedthrough the switch 611 has a given plane of polarization, such lightwill be transmitted through the half wave plate 615 and birefringentplate (calcite) 610 to appear at the same relative positions as theyoriginally appear in the display 602. If such pixels are, respectively,red, green and blue pixels of a triad, such pixels may be at thelocations of the pixel images 620 r, 620 g, 620 b shown in FIG. 34.However, when the plane of polarization of the light exiting the switch611 is such that it is appropriately rotated by the half wave plate 615so as to impinge on the calcite 610 in a direction relative to the axis610′ to cause shifting of the light output, such pixels will appear asimages 620 r′, 620 g′, 620 b′. Thus, it will be seen that the offset orshifting is in a sense diagonal rather than horizontal or vertical. Theangle at which such diagonal occurs relative to horizontal, for example,depends on the magnitude of the angle theta. Thus, it will beappreciated by appropriately selecting the angles of the respective axisof the components and their relationship to each other, whereas desireddirections of shifting can be obtained. Also, the extent or distance ofsuch shifting can be determined, for example, by the thickness of thebirefringent device 610, i.e., the effect of optical thickness thereofhaving an affect on the light transmitted there through.

Referring to FIGS. 35 and 36 and the Chart I below, an optical displaysystem 640, which includes two active dithering systems 641, 642 and onepassive dithering system 643 is illustrated. The optical system 640receives plane polarized light input 644 from a display 645. If thedisplay 645 is not the type that provides a plane polarized lightoutput, than an additional polarizer 646 may be used to provide suchplane polarization. The orientation of respective components of thedisplay system 640 is depicted by respective double-headed arrows abovethe various components.

The display system 640 may be used to provide a video output displayoperation. In an exemplary video display system, such as an NTSC or PALsystem, it is conventional to compose a picture or a frame from twointerlaced and sequentially presented fields (sometimes referred to assub-frames). The optical display is able to produce four outputconditions and signals in the manner described below. Such four outputconditions may correlate to two respective frames and the two respectivefields in each frame in a video display system, such as a televisionsystem using a liquid crystal display or some other display as the imagesource. However, it will be appreciated that the four output conditionsdescribed below may be correlated with the operation of other types ofdisplay systems or with a video display system in a way different fromthe exemplary operation described below.

In the optical system 640 the active dithering system 641 includes aswitch 650 and a birefringent device 651. The active dithering system642 includes a switch 652 and a birefringent device 653. The passivedithering system 643 includes a quarter wave plate 654 and a thirdbirefringent device or material 655. The first and second switches 650,652 may be respective surface mode birefringent liquid crystal cells orsome other switch as is described elsewhere herein. The first, secondand third birefringent devices 651, 653, 655 may be calcite material orsome other birefringent material having axis oriented generally in themanner illustrated and tipped in the manner described above.

In describing operation of the optical display system 640, reference ismade to a pixel of the display and light representing that pixel. Thepassive dithering system 643 effectively doubles the size of the pixelreceived by it from the display 645 and via the respective activedithering systems 641, 642. Therefore, as is seen in FIG. 36, each pixelinput to the passive dithering system 643 is shown in solid lines andthe doubled image thereof is shown in dotted lines adjacent thereto. Forexample, the pixel provided the passive dithering system 643 for thefirst field of the first frame is represented at 660, and the ditheredimage 660′ is shown adjacent thereto in dotted lines. The passivedithering system operates in the manner of the passive dithering systemsdescribed above, for example.

Referring to the Chart I below, at frame 1, field 1, the voltage orenergization of the first switch 650 is low so that the switch rotatesthe plane of polarization of the input vertically polarized light tohorizontally polarized light as the output there from; see the columnlabeled “polarization direction output 1” having the letter “H”representing such horizontal polarization. Delivery of that horizontallypolarized light to the first calcite 651 results in no shift oflocation. Continuing in the first line for frame 1, field 1 in the ChartI below, the voltage of the second switch 652 is low, whereby thatswitch rotates the plane of polarization back to vertical, as isrepresented by the letter “V” in the column labeled polarizationdirection output 2; and, therefore, the second calcite member 653 doesnot shift the location of the pixel. When the vertically polarized lightoutput from the second calcite 653 enters the quarter wave plate 654,such light is divided into horizontal and vertical polarized components;the vertically polarized component transmits through the third calcitematerial 655, and the horizontally polarized component is shiftedhorizontally thereby effectively doubling the size of the pixel andproducing the image 660′, as is represented in the last column of thetable designated calcite 3 shifting and doubling in the horizontaldirection the particular pixel.

The second field of the first frame, for example, each pixel of thesecond frame, is displaced vertically relative to the correspondingpixel of the first field of the first frame. The pixel 661 representsthe location of such downwardly vertically displaced pixel for thesecond field of the first frame when the display system is a video typeusing interlaced fields to produce a frame. The second line of the ChartI below shows the conditions of the surface mode switches 650, 652, bothbeing at high voltage so as not to rotate the plane of polarization oflight transmitted there through, the resulting vertical downwarddisplacement caused by the first calcite 651, and the doubling of thepixel by the passive dithering system 643 to produce not only pixel 661but also the dithered pixel 661′. In pixels 660, 660′, the two digitsone in each represent, respectively, first frame, first field; and inthe pixels 661, 661′, the digits one and two represent first frame,second field, respectively.

Lines three and four of the Chart I below represent conditions andshifting resulting from those conditions of the switches 650, 652,direction of plane of polarization, etc. as was described above withrespect to the first two lines of the Chart I below in order to achievepixels 662, 662′ and 663, 663′, the primed pixels representing thedithered images that doubles the effective size of the overall pixel,such as the doubled size 663 plus 663′. As was mentioned above, theamount of shifting or translating of a particular pixel may be afunction of the birefringence and/or optical thickness of the respectivebirefringent device, such as the respective calcite plates 651, 653,655. Also, in a conventional video system there usually is no horizontalinterlacing. The two field of the second frame represented by pixels662, 662′, 663, 663′ may represent images moved to fill optical deadspace, images to effect super imposing respective colors, as isdescribed further below, or some other purpose. The increasinglyeffective size of each pixel, such as by doubling it to increase pixel660 to the effective size of the sum of pixels 660, 660′, can be used toimprove resolution by effectively covering optical dead space in thedisplay. The vertical displacing of pixels can be used to cause a liquidcrystal display to provide a true or more nearly true interlacedoperation whereby a pixel presented in one field of a frame is presentedat a different location when the second field of that same frame isproduced.

An advantage to the use of a dithering system with a display, such as aliquid crystal display, wherein the location of a pixel in the outputcan be shifted even though the actual location of the pixel in thedisplay itself, such as an LCD, remains fixed is that correct data canbe used to drive the pixel to provide the desired image output withrelatively accurate following of the video signal. In a conventional LCDused to provide a video output a particular pixel may average the twofields of a frame; the average is not an accurate representation of thedata received from the video signal. However, using a dithering systemin accordance with the present invention, a pixel of the LCD may bedriven based on information from the video signal intended to drive thatpixel for a particular field of a frame to provide a visual output fromthe display system, such as display system 640. Subsequently when theimage output of the respective pixel is shifted so that it is in thelocation desired for the second field of the particular frame, theactual information from the video signal that ordinarily would be used,say in a CRT, for example, could be the information that is used tooperate or to drive the pixel which then provides a relatively accurateoutput representative of the appropriate input signal.

Using the two active and one passive dithering systems of the opticaldisplay system 640 is it possible to obtain eight copies of the originalimage, if desired, namely that provided at pixel 660, for example. Sucheight copies may be obtained for every field for every frame, if desiredand, thus, provide a macro pixel effectively about eight times the sizeof the pixel 660. In another embodiment, the data picked off theincoming analog signal or other video signal that operates the pixel660, e.g., to turn it on or off, may be selected at the appropriate timeto drive the pixel 660; and subsequently the pixel 661 may be operatedas a function of information picked off the incoming video or analogsignal representing the desired operation of the pixel 661 forinterlaced fields operation of a conventional NTS or PAL system.However, additionally, if desired, the information from the incomingsignal also could be picked off to represent the on/off or intensityeffect of a pixel presented at location of pixel 662 accurately torepresent that pixel even though that pixel physically may not be in thedisplay 645 but rather is represented by the pixel of the display 645that produces pixel image 660 shifted to the location of pixel 662. Inother words, in an exemplary LCD there may be two relatively adjacentpixels, and the information from the incoming video signal would bepicked off from that video signal to drive the respective pixels at theappropriate times. However, there also may be information contained inthe video signal that would represent a desired optical output from theoptical display system 640 from a pixel located between the twomentioned pixels. The present invention allows the information from thevideo signal that would be used to drive such intermediate pixel to bedelivered to the pixel of the display 645 that would produce pixel image660 while the dithering systems in the optical display system 640 effecthorizontal or lateral displacement of the optical output to a locationwhere such intermediate pixel might otherwise appear in the output imagefrom the optical display system 640. This operation can enhance theresolution provided by the optical display system 640 and the accuracyof representation of the information carried by the input video signal,etc.

Superimposed Color Operation

Referring to FIG. 37 there is a shown a layout of an exemplary group ofred, green and blue pixels of an exemplary liquid crystal display. Thepixels are arranged in respective parallel rows and columns. Capitalletters represent the color of the pixel, e.g., whether the pixel willdeliver output like that is red, green or blue. Portions of two rows areshown.

In the viewing of a color liquid crystal display the eye of the viewer,i.e., a human eye, may receive light input from many different pixels,and the eye effectively integrates the light inputs. One way ofconsidering such viewing is to analogize the adjacent pixels, which areextremely small, effectively being superimposed so that the light therefrom is superimposed. Therefore, the combination of red, green and bluelight that is superimposed would provide a white light as seen by theviewer.

The various embodiments of dithering systems in accordance with thepresent invention, including those disclosed and equivalents thereof,may be used to effect real superimposing of respective pixels, therebyenhancing the color output or color response of a color liquid crystaldisplay. Such superimposition is depicted in FIG. 37 and now isdescribed. The two rows of pixels shown in FIG. 37 are portions ofrespective rows of pixels in a color liquid crystal display. In thefirst row shown there are five pixels of the indicated colors; and inthe second row there also are five pixels of the indicated colors. Thesequence of colors is red, green and blue in both rows, but the sequenceis offset by one pixel one row to the other. Therefore, in the first(top) row the first pixel row, and in the second row the first pixel isgreen. The arrangement of pixels in FIG. 37 is exemplary. Many othertypes of arrangements of pixels may be used whether in parallel rows andcolumns in the manner shown, in a so called delta configuration orpattern wherein there is an offset of rows, such as in FIG. 40, etc.

Using the optical display system 640, for example, the red pixel Ra atthe top left of FIG. 37 is duplicated by the passive dithering system643 to produce a red pixel or ra, which is represented in dash lines.Operation of the first dithering system 641 produces a second copy ofboth those red pixels displaced downward to locations of dash red pixelsdesignated ra′. Such operation of the first dithering system 641 iscoordinated with the second dithering system 642 to effect such downwardshift. Similarly, horizontal shifting of all four red pixels justmentioned, namely Ra, ra, and the two designated ra′ to a horizontallyshifted or laterally shifted place results in the red pixels representedby dash lines and designated ra″, one of which is superimposed over thegreen pixel Ga and one of which is superimposed on the blue pixel Ba.Such shifting may occur in a time sequence that is sufficiently fastthat the human eye does not perceive the various shifts. Additionally,such shifting occurs in a time sequence coordinated with the desiredcolor output from the display as represented by the input video signalsto the display so that the superimposed colors provide a good qualityand accurate representation of the color output from the displayintended as a result of the input video signal. Similarly to the justdescribed shifting of the red pixel Ra, shifting of the green pixel Gaalso occurs, and such shifted pixels are represented by dotted outlineat pixel locations represented by Ga due to the passive dithering system643, and the other shifted pixels represented by dotted lines labeledga′ and ga″ resulting from coordinated operation of the active ditheringsystems 641, 642. Furthermore, similar operation occurs for the bluepixel Ba, which is represented by phantom lines at pixels or pixellocations designed ba, ba′, and ba″. The four blue pixels represented byrespective designations ba′ and ba″ near the bottom of FIG. 37 wouldoverly or be superimposed on other pixels which are not shown in orderto simplify the drawing and description.

Briefly referring to FIG. 38, shifting of the red pixel R intorespective gaps and also superimposed on other pixels is shownschematically and simply. Specifically, pixel R is doubled by thepassive dithering system 643 of the optical display system 640 in FIG.35, for example to provide pixel r. Both pixels R and r are duplicatedalso at pixel image locations r′ shown in FIG. 38 in the gap betweenrespective parallel rows of actual pixels. Pixels R, r and r′ also areduplicated to the right relative to the illustration of FIG. 38 as pixelimages r″, some of which are in the same gap as pixel images r′ and oneof which overlies or is superimposed on the green pixel G. Thus, it willbe seen that the pixels can be shifted to various locations in thedisplay to achieve the desired optical output.

As the display of FIG. 38 is operated as part of the optical displaysystem 640 to duplicate pixel images and/or to translate pixel images,so, too, the display shown in FIG. 39 represents similar modifiedoperation of the optical display system 640. In particular, in FIG. 39lateral shifting occurs like that in FIG. 38; but in FIG. 39 thevertical shifting of images results in the shifted image overlying thegap between adjacent rows of pixels of the display 645 and alsooverlying at least a portion of the pixel of the display 645 which isvertically displaced beyond such gap between pixel rows. Placing thepixel image in a gap increases the fill factor of the display. As wasmentioned above, the shifting may result in superimposing pixel imagesto achieve the superimposed color response described above. Also, ifdesired, the vertical shifting may result in a portion of the shiftedpixel image still overlapping a portion of the image in the originalrow, such as the illustrated pixel R and shifted pixel image r′ therebelow. Such superimposing of pixels may provide a desired type of visualoutput for the optical display system 340.

Briefly referring to FIGS. 40 and 41, there is shown a delta design ofpixel layout for a display in FIG. 40, such as an LCD 645 and the outputimages there from after transmitting through an optical display system680, which includes one active dithering system 681 and two passivedithering systems 682, 683. The active dithering system 681 includes aswitch, 684, such as a birefringent liquid crystal cell, and a calcitecrystal 685 able to transmit an image or to shift the image verticallypixel, depending on the direction of plane of polarization of lightincident thereon. The passive dithering system 682 includes a half waveplate 686, which rotates the plane of polarization of incident light 45degrees, and a second calcite crystal 687, which can transmit theincident pixel image and has a thickness, birefringence, axialorientation and tipped to displace the image ½ triad pitch horizontally.The passive dithering system 683 includes a half wave plate 688, whichrotates the plane of polarization of incident light 45 degrees, and asecond calcite crystal 689, which can transmit the incident pixel imageand has a thickness, birefringence and axial orientation and tip to beable to displace the image ½ pixel pitch horizontally.

The optical display system 680 and dithering systems 681, 682, 683thereof are set up to effect shifting ½ triad pitch to the right; 1pixel pitch left and ½ pixel vertical pitch down. This arrangement isrepresented by only the blue pixel Ba. In shifting that pixel ½ triadpitch to the right, pixel ba results. In shifting both pixel Ba and ba 1pixel pitch to the left, two respective pixel images ba′ areproduced—one is superimposed over the green pixel G, and one is in thegap between the blue pixel Ba and the red pixel R horizontally adjacentto the blue pixel Ba. Such shifting provides both for filling theoptically dead space and effecting a superimposing of respective colorpixel images as was described above. The shifting of pixel imagesvertically to form the four pixel images ba″ places some of those in thegaps between rows of pixels and some in superimposed relation to thesame and/or other pixels or shifted pixel images.

Referring to FIG. 42, a person 704 is shown wearing a head mountedviewing system 705 in accordance with the present invention. The viewingsystem may be part of a virtual reality viewing system having one ormore displays which are viewed by the person. The viewing system may bepart of a telecommunications system, entertainment system, or some otherdevice in which light, optical, etc. information can be presented forviewing, projecting, photographing, or other use. Exemplary systems inwhich the invention may be used are disclosed in the above-mentionedpatent applications; of course there may be other uses, too.

The head mounted viewing system 705 includes a housing 705 h in whichthe various components of the viewing system 705 are included, and amounting device 705 m, such as a strap, eyeglass or goggles type framesupport structure, etc. The mounting device 705 m mounts the housing 705h for support from the head of the individual 704 placing the viewingsystem 705 in position in front of one of the eyes for viewing of animage presented by the viewing system 705. Whether the viewing system705 is hand held, head mounted, or otherwise supported, for example,from a pedestal, tripod, frame, etc., from a table, from the floor, froma console 9, etc., preferably the viewing system 705 and housing 705 hthereof is relatively small and sufficiently lightweight to facilitatemoving, transporting, mounting, and/or holding. If the viewing system705 is to be hand held or head mounted, it especially should berelatively lightweight to avoid being a weight burden on the hand orhead of the individual using the viewing system 705. Also, to facilitateholding the viewing system 705 manually or head mounting the viewingsystem, the viewing system 705 should be relatively small. An exemplaryviewing system may be, for example, approximately 4 to 5 inches inheight, approximately 2 to 3 inches wide, and approximately 1½ to 2inches deep. These are exemplary only, and it will be appreciated thatother dimensions may be used.

In using the viewing system 705 it may be head mounted, hand held,coupled to a control box, console or the like, for example, similar tothe main body of the conventional telephone when used in atelecommunication system.

Turning to FIG. 43, the viewing system 705 is shown in detail as amonocular viewing system. The housing 705 h includes a viewing portion711 and a support portion 712. The viewing portion 711 is intended to beviewed by an eye 713 of a person 704 (FIG. 42), and the support portion712 is intended to be held in the hand of that individual. As wasmentioned above, a head mount 705 m may be provided to support theviewing system 705 from the head of a person. Thus, the housing 705 hmay be hand held, supported by a strap, cap, temple piece as ineyeglasses, or otherwise mounted for viewing by a person.

The viewing system 705 includes an optical system 714 in the housing 705h. The optical system 714 includes an image source 715, such as an LCD,that provides images for viewing by the eye 713 through a viewing port716. A viewing lens 717 (or group of lens) presents to the eye 713 animage which appears at a comfortable viewing distance, such as about 20inches or more away. An image resolution enhancing device 18 (sometimesreferred to as an optical line doubler or OLD, dithering device orsystem, EDS, etc.) optionally included in the optical system 714 may beused to enhance the resolution or other qualities of the image producedby the image source 715.

A number of optical components 720 are included in the optical system714. The optical components include focusing optics 721 (sometimesreferred to simply as “lens” or as projection optics or as a projector),a beam splitter 722, and one or more retro reflectors 23, 23′.

The image source 715 includes a display 724 d and a source of incidentlight 724 i. The light source illuminates the display 724 d, and thedisplay in turn presents images which can be projected for viewing bythe eye 713, as will be described in greater detail below. It will beappreciated that other types of image sources may be used, examplesbeing cathode ray tube displays, other liquid crystal displays, plasmadisplays, etc. Examples of several displays and light sources arepresented in the above-referenced co-pending patent applications. Aconnection cable 28 provides electrical and/or optical signals and/orpower to the optical system 714, and is particular to the image source715 and OLD 18 to develop the above-mentioned images for viewing by theeye 713. A control system 729 is coupled to the cable to provide suchelectrical signals for controlling operation of the display system 705,as is described in further detail below.

Summarizing such controlled operation, though, the display 724 d may bea twisted nematic liquid crystal display, and the OLD 18 includes anoptical switch, such as a surface mode liquid crystal cell, thatswitches polarization characteristics of light to cause the light outputto viewed by the eye 713 to be, for example, of enhanced resolution, asis described further below. Therefore, the control system 729 providessignals to generate the image by the display 724 d; and the controlsystem 729 also controls the optical switch to effect a synchronizationsuch that there is a phase or time delay between the signals to thetwisted nematic LCD and the signals to the optical switch. Accordingly,the optical switch which operates at a different speed, e.g., faster orin shorter time than the twisted nematic LCD will be coordinated withthe operation of the twisted nematic LCD to improve operation andoptical output of the display system 705. Detailed operation of thecontrol system is described further below, for example, with respect toFIGS. 44-46 and 48.

Dithering may refer to the physical displacement of an image. Thedithering system 718 may be an electro-optical dithering system (EDS),which refers to an electro-optical means to physically shift or tochange the location of an optical signal, such as an image. The shiftingmay result in doubling of the number of pixels or scan lines of adisplay—thus, reference to OLD (optical line doubler). The shifting alsomay result in quadrupling (or more or less increase) pixels or scanlines; and in such case OLD also may be used as a generic label. Theshifting may be active in response to an electrical, magnetic or otherinput. The dithering system 718 may be passive, e.g., in which shiftingoccurs constantly or substantially constantly (or continuously); inother words such shifting may occur all the time without the need for aseparate input to cause shifting. Various embodiments of ditheringsystems useful in the invention are described above.

The image may be shifted along an axis from one location to another andthen back to the first, e.g. up and then down, left and then right, orboth, etc. The optical signal may be moved in another direction. Thedithering may be repetitive or periodic or it may be asynchronous inmoving an image from one location to another and then holding it there,at least for a set or non-predetermined time. Also, as was mentioned,the dithering may be passive, and, thus, constant, e.g., withoutchanging. When the dithering is passive there usually are providedsimultaneously the original image at the undithered location and asecond or dithered image at another location, e.g., located adjacent orspaced apart from the undithered image.

Referring to FIG. 44, the top line A in the graph represents anelectrical signal, namely the voltage applied to a given display pixel(sometimes referred to as picture element or component) as a function oftime. The pixel may be a part of a twisted nematic type LCD, such aspart of the display 724 d, especially an active matrix LCD, although thepixel may be a part of some other type of display, optical device, etc.When the voltage is applied to an active matrix display, it results inan electric field being applied across the liquid crystal materialcausing a particular type of operation, e.g., alignment with respect tothe field or when no field is applied relaxing to an alignment which maybe influenced, for example, by the surfaces, surface coatings, etc., ofthe liquid crystal cell or device forming LCD. The voltage A illustratedin FIG. 44 is applied at a frequency of 60 Hz.

The second line B in FIG. 44 represents the desired light transmissioncharacteristic of an ideal pixel as a function of time. In theillustrated example, the pixel is switched between clear (sometimesreferred to as the white state) and dark (sometimes referred to as theblack state). As illustrated, the clear state would occur when thevoltage A is high, and the dark state would occur when the voltage A ishigh.

In the illustrated case of an ideal pixel in FIG. 44, the pixel switchestransmission B from dark to clear at the same time the voltage switchesfrom high to low. That is, the ideal pixel switches in phase with theapplied voltage A. Furthermore, in the OLD or EDS 1, etc. (FIGS. 1, 2-6,11-12, etc.) hereof (hereinafter referred to as EDS 1 for brevityalthough such reference includes the various embodiments of active andpassive dithering systems disclosed herein), the position of the pixelchanges by switching the voltage applied to the surface modebirefringent liquid crystal cell, optical switch or polarization rotator11 (FIGS. 1, 5 and 6, for example). Therefore, it follows that in theideal case, i.e., for use with the ideal pixel, the voltage applied tothe optical switch 11 also would be switched synchronously with thevoltage A applied to the ideal pixel and in phase.

However, a real liquid crystal display 20, 724 d utilizing the twistednematic effect cannot switch between transmission states as rapidly asindicated in the second line B of FIG. 44. For example, the activematrix liquid crystal display used in the Sony XC-M07 monitor can switchfrom dark to clear in about 20 milliseconds and from clear to dark inabout 11 milliseconds. Switching time is defined conventionally as thetime required for the transmission to change between 10% and 90% of thefinal values. This real switching behavior is illustrated in the thirdline C of FIG. 44. In this third line C depicting light transmission,the transmission of the clear state has been normalized to 100% and thetransmission of the dark state has been normalized to 0%. It will beappreciated that the graph line C is schematic only, and the precisetimes mentioned above are not necessarily accurate.

In FIG. 45 the graphs present information similar to that presented inthe graphs of FIG. 44 except that in the graphs of FIG. 45 the frequencyof the applied voltage A′ to the pixel, e.g., of the display 724 d, isdoubled to 120 Hz. The transmission B′ of the ideal pixel in FIG. 45 isshown synchronized and in phase with the applied voltage A′. However,the actual transmission C′ of a real pixel is illustrated in the thirdline of FIG. 45. As is shown, within the available time of respectivehalf cycles of the applied voltage A′, the real pixel is able to switchtransmission between about 25% and 75%. This means that the contrastratio would be reduced by a factor of about one half (½) compared to the60 Hz case of FIG. 44. This behavior is characteristic of many twistednematic effect LCDs; starting at a modulation of about 60 Hz. everyincrease in the frequency of the applied voltage by a factor of two (2)usually results in a reduction in the contrast ratio by a factor ofabout one half (½).

Referring to FIG. 46, line A″ represents the applied voltage to thepixel at 120 Hz. The second line C″ represents the transmission responseof a real pixel of an active matrix twisted nematic LCD. Note that lineC″ is similar to line C′ in FIG. 45. A guide line D has been drawn inthe graph of line C″ in FIG. 46 at 50% transmission. That portion of aparticular frame, in which the real pixel is presenting an image ofclear or dark, having a transmission greater than 50% is defined here asthe clear state. That portion of the frame having a transmission lessthan 50% is defined here as the dark state. As seen, the real pixel doesshutter light at 120 Hz but the transmission modulates between 25% and75% rather than the 0% to 100% experienced when the frequency of theapplied voltage signal A was 60 Hz. in FIG. 44.

Another feature of the 120 Hz response of the real pixel is shown inFIG. 46. Consider the point marked along the time scale by the doubleheaded arrow E. The bottom part of the arrow E indicates the point intime that the transmission of the real pixel switches from dark toclear; the top of the arrow E indicates the corresponding appliedvoltage. It can be seen that the applied voltage A″ is out of phase withthe transmission characteristics of the pixel, i.e., when the real pixelswitches between what is considered the clear state and the black state,by 90□.

In the present invention the EDS 1 may be adjusted to introduce asimilar phase shift in the voltage F (FIG. 46) applied to the opticalswitch 11. An exemplary optical switch 11 is a surface mode birefringentliquid crystal cell. Such device usually can switch between states inresponse to a change in input signal much faster than does a twistednematic liquid crystal cell or LCD. Therefore, by introducing theindicated phase shift in the driving of the surface mode liquid crystalcell and the twisted nematic LCD, the optical switch can be coordinatedto switch optically at the same time that the LCD 724 d, for example,switches optically from what is considered its clear state to what isconsidered its dark state or vice versa. As a result, as the EDS 1operates in coordination with the LCD 724 d, for example, to crispnessor sharpness of the output image can be improved and there is lesslikelihood of a bleeding effect between images produced by pixels whichare periodically optically shifted using the dithering principles of anOLD or the like.

After the phase of the surface mode liquid crystal cell optical switch11 has been adjusted as described, the contrast of the display 724 dwould be reduced by a factor of about one half (½) when the display isoptically doubled and one fourth (¼) when the display is opticallyquadrupled. The decrease in contrast is due to the increased frequencyat which the display liquid crystal cell (LCD) is driven, not due to theEDS or how it is driven. It has been found that the contrast reductionis nearly undetectable by the human eye and, therefore, has been foundacceptable for many applications.

It will be appreciated that although the above description regardingFIGS. 44-46 presents phase shift of 90□ for the indicated purpose, theprinciples of the invention may be used to introduce other phase shiftsto achieve a similar coordination between two optical devices which havedifferent response characteristics, such as, for example, change inlight transmission or polarization as a function of change in electricalinput, or other input, e.g., magnetic input.

In FIG. 47 details of optical components of the optical system 714 ofthe display system 705 are shown. The optical components shown in FIG.47 are similar to those included in the housing 705 h of FIG. 43;however, in FIG. 47 the housing 705 h and support 705 m are not shown tofacilitate illustrating the invention and to simplify the drawing.

The optical components 720 of the optical system 714 include focusingoptics 721 (sometimes referred to simply as “lens” or as projectionoptics or as a projector), a beam splitter 722 and retro-reflector 723.The display system 705 also may include an image source 715 (FIG. 43)which provides images or light having characteristics of an image and,if desired, may be part of the mentioned projector. An exemplary imagesource is a liquid crystal display, such as a small liquid crystaltelevision having a cross-sectional display area on the order of aboutone square inch or less. As shown, the image source 715 includes aliquid crystal display 724 d which modulates light from the light source724 i to form images for viewing by the eye 713. Alternatively, theimage source may be separate and simply used to provide one or moreimages or light having image characteristics that can be provided by theviewing system 705, such as that shown in FIG. 1, or a head mounteddisplay, sometimes referred to as HMD to the eye 713. Additional opticalcomponents of the optical system 714 may include linear polarizers,circular polarizers, wave plates, focusing elements, such as lenses ormirrors, prisms, filters, shutters, apertures, diaphragms, and/or othercomponents that may be used to provide a particular type of output imagefor viewing by the eye 713. Examples of several embodiments using suchadditional optical components are described below with respect to otherdrawing figures.

The invention is useful with virtually any type of image source ordisplay source. An example of such a display source is a compact flatpanel display, and especially one utilizing a reflective liquid crystaldisplay made from a single crystal silicon active matrix array.

In FIG. 47 the image source 715 displays an image 825, which is shown inthe drawing as an arrow 826. The light 827 leaving the image source 724represents an image or has characteristics of an image, and that lightis collected by the focusing optics 721 of the optical system 714 of thedisplay system 705 and travels to the beam splitter 722. In FIG. 47 andin a number of the other drawing figures hereof the focusing optics 721is represented as a single lens. However, it will be appreciated thatthe focusing optics 721 may include one or more other components, suchas lenses, reflectors, filters, polarizers, wave plates, etc.

Although the image source(s) 715 is shown in FIG. 47 located relativelyabove the beam splitter 722, the image source may alternatively belocated below the beam splitter as is shown in FIG. 2.

At least some of the light 827 a incident on the beam splitter 722 isreflected by the beam splitter as light 827 b toward the retro-reflector723. The retro-reflector may be, for example, a screen made ofretro-reflecting material. Exemplary retro-reflectors are well known.One example is that known as a corner reflector or a sheet having aplurality of corner reflectors. Another example is a material havingplural glass beads or other refracting and/or reflecting devices on orin a support. An example of a retro-reflector is a film or sheetmaterial having a plurality of corner cubes which material is sold byReflexite Corporation of New Britain, Conn. Such material is availablehaving about forty-seven thousand corner reflectors per square inch.

The light (light rays) 827 c, which are shown as broken lines, arereflected by the retro-reflector 723 such that their path is exactlyback along their direction of incidence on the retro-reflector. In thisway some of the light rays 827 c pass through the beam splitter 722 andare directed toward a location in space designated 828 in theillustration of FIG. 47. The eye 713 of a viewer (person) can be placedapproximately at location 828 to see the image, and the pupil and lens,individually and collectively designated 713 a, of the eye, accordingly,are shown at that point. The lens 713 a focuses the light incidentthereon as an image on the retina of the eye 713.

The projection lens 720 projects light toward the retro-reflector 723 tocause a real image to be formed at the retro-reflector or in front orbehind the retro-reflector. As is defined in Jenkins & White,Fundamentals Of Optics, McGraw-Hill, 1976, for example, using anexemplary projection lens, an image is real if it can be visible on ascreen. The rays of light are actually brought to a focus in the planeof the image. A real image is formed when an object is placed beyond thefocal plane of a lens; the real image is formed at the opposite side ofthe lens. If the object is moved closer to the focal plane of the lens,the image moves farther and is enlarged. In contrast, a virtual imageoccurs if an object is between the focal point of a lens and the lensitself.

In FIG. 47 the broken lines represent light rays which travel afterreflection by the retro-reflector along the same or substantially thesame path, but in the opposite direction to, respective incident lightrays impinging on the retro-reflector. Thus, the retro-reflector 723 ispart of a conjugate optics path 823 a in which light incident thereon isreflected in the same path and opposite direction as reflected light.The beam splitter 722 directs light from the focusing optics 721 intothat conjugate optics path and toward the retro-reflector; and the beamsplitter also passes light in the conjugate optics path from theretro-reflector to the output port 16 (FIG. 2) for viewing by the eye713. The beam splitter 722 and retro-reflector 723 cooperate as aconjugate optics system to provide that conjugate optics path.

Using the described conjugate optics path and system, relatively minimalamount of the light from the image source 724 and focusing optics 721 islost and, conversely, relatively maximum amount of light is directed tothe eye 713. Also, there is substantial accuracy of image and imageresolution conveyed to the eye. Furthermore, especially if a relativelygood quality retro-reflector is used so that the precise location atwhich the image 830 is in focus will not be critical, e.g., it can bebehind or in front of the retro-reflector, the tolerance required forthe relative positioning of the components of the optical system 714 isless severe. This makes the HMD display system 705 relatively robust andreliable.

In FIG. 47 the viewed image 830 is represented by an enlarged arrow 831.Such arrow 831 is shown in FIG. 47 as a magnified focused image of theimage 825 from the image source 724. The image 830 may be in focus at orapproximately at the retro-reflector 723, and this is especiallydesirable for good quality images to be provided the eye 713 when arelatively low quality retro-reflector is used. A low qualityretro-reflector is one which has relatively low resolution or accuracyof reflecting light in a conjugate manner in the same path but oppositedirection relative to the incident light. With a low or poor qualityretro-reflector and the image not being focused at the retro-reflector,it is possible that too much light may be lost from the desiredconjugate optics path back to the eye 713, and this can reduce thequality of the image seen. However, the image 830 may be in focus atanother location or plane either behind the retro-reflector (relative tothe eye) or in front of the retro-reflector, and this is easier to dowhile maintaining a good quality image for viewing when theretro-reflector is a good quality one. The better the retro-reflector,the more self-conjugating is the optical system 714 and the less theneed to focus with precision at the retro-reflector.

Retro-reflector quality may be indicated by the radians of beam spreadof light reflected. For example, a relatively good qualityretro-reflector may have from zero or about zero radians of beam spreadto a few milliradians of beam spread. The quality usually is consideredas decreasing in proportion to increasing beam spread of reflectedlight.

In considering the brightness of the image seen by the viewer, thenature of the beam splitter 722 plays a role. The light produced by theimage source 724 may be polarized or unpolarized. If the beam splitter722 is of a non-polarizing type, then a balanced situation is to have50% of the light incident on the beam splitter 722 be reflected and 50%transmitted. Thus, of the light 827 a incident on the beam splitter 722,50% is reflected and sent toward the retro-reflector screen 723 as light827 b. Of the reflected light 827 c from the retro-reflector 723, 50% ofthe light will be transmitted through the beam splitter 722 and willtravel to the viewer's eye 713. This configuration of the opticalcomponents 720 of the display system 705 can transfer to the viewer'seye a maximum of 25% of the light produced by the image source 724. Ifdesired, the beam splitter 722 can be modified in ways that are wellknown to change the ratio of the reflected light to transmitted lightthereby. Also, the beam splitter 722 may include an anti-reflectioncoating so that all or an increased amount of the image comes from oneside of the beam splitter and thus to reduce the likelihood of a doubleimage.

Since the optical system 714 of the display system 705 provides goodresolution of the image and maintains the characteristics thereof, theimage source can be a relatively inexpensive one that does not have tocompensate for substantial loss of image quality that may occur in priordisplay systems. Furthermore, since a relatively large amount of thelight provided by the image source 724 is provided to the eye 713 forviewing, e.g., since the retro-reflector can virtually focus the lightfor viewing at the eye, additional brightness compensation for loss oflight, as may be needed in prior display systems, especially portable,e.g., hand held or head mounted, ordinarily would not be required.

For exemplary purposes, in FIG. 47 three light rays 840 a, 840 b, 840 c(collectively 840) originating at the tip of the arrow 826 constitute aportion of the light 827. Three light rays schematically shown at 841 a,841 b, 841 c (collectively 841) also are examples of light emanating atthe tail of the arrow 826. The light 827 has characteristics of theimage 825 from or provided by or at the image source 715, andrepresented by the exemplary light rays 840 and 841, is focused by thefocusing optics 721 onto the retro-reflector 723. The size of the image830 seen as the arrow 831 on the retro-reflector 723 depends on thefocal length of the focusing optics 721 and the distances between theimage source 724 and the retro-reflector 723 from the focal points 843,844 of the focusing optics 721. Thus, magnification can depend on suchfocal length. The image source 715 should be located relative to thefocusing optics 721 such that an image can be focused, e.g., in focus asis shown in FIG. 47, at or approximately at the retro-reflector. Forexample, the image source 715 may be beyond the focal point 843 of thefocusing optics 721, and the retro-reflector likewise preferably isbeyond the focal point 844 of the focusing optics so that the image canbe focused at the retro-reflector.

In the illustration of FIG. 47 the image 830 on the retro-reflector 723is magnified relative to the size of the image at the image sourcedisplay 724 d; it does not have to be magnified. The image 830 may bethe same size as the image 825 or it may be smaller. Thus, although theimage source display 724 d may be relatively small and/or may provide arelatively small size image 825 at its output, the size of the image 830viewed by the eye 713 may be different.

The optical system 714 is operable to place the image plane effectivelyat the retina of the viewer's eye 713. This is accomplished byeffectively putting the plane of the eye lens (or pupil) 713 aeffectively at the position occupied by the focusing optics 721 relativeto the source of the image provided to the focusing optics. In a sensethe lens 721 is optically superimposed on the lens 713 a of the eye 713.

The invention provides an optical system in which there are conjugatepaths from a lens, such as focusing optics 714, which corresponds to the“lens means” of an optical sensor, e.g., the eye 713. Stated in anotherway, the invention presents visual information or optical data with awide field of view by taking the output from a lens (focusing optics721) and reflecting the light back along a conjugate path toward alocation corresponding to that of the same lens which was in theoriginal path, but actually direct that reflected light onto the eyeplaced at such corresponding location. This is obtained by using theconjugate optics arrangement disclosed herein.

The human eye is most comfortable when viewing an image at a distance ofabout twenty inches, approximately at the distance at which one wouldplace a book, document, etc. to be read. It is desirable that the finalimage as seen by the viewer be located at such distance, e.g.,approximately twenty inches from the pupil 713 a of the eye. This can beaccomplished in the manner, if desired, by adding an additional lens 717(FIG. 43) or other optical system (not shown) between the beam splitter722 and the eye 713. Such lens may cause the person to see a virtualimage behind the retro-reflector, as is described in several of theabove patent applications. Although in many viewing devices furtherspacing between the eye and the optical component of the optical systemnearest the eye may be desired to obtain desired eye relief, the use ofthe lens 717 at the indicated distance of about ½ to 1 inch from the eyeusually is acceptable and reasonably comfortable because that is theapproximate spacing of ordinary eye glasses to which people ordinarilyrelatively easily become accustomed.

The function of the lens 717 may be obtained by using a negative lens atthe focusing optics 721.

Referring to FIG. 14 an EDS 201 in the form of an electro-opticaldithering system which includes two line doublers in optical series isshown used with a display 202, in the illustrated embodiment an LCD(although other types of displays can be used), as a display system 203.The display 202 and the EDS 201 may be substituted for the display 724 dand EDS 1 in the display system 705 of FIGS. 42 and 43. The display 202may include a light source or a separate light source 724 i may be usedto illuminate the display 202.

FIG. 48 presents a number of graphs representing signals in the controlsystem 729 for the display system 705 or display system 203 to presentan image that is enhanced by optical dithering (optical line doubling,in fact quadrupling) and that is enhanced by the phase shifting of theinvention as described herein. The respective signals are shown on atime scale presented on the “x” axis. Vertical sync pulses G from aconventional video signal used for driving a television, CRT, LCD, etc.,are presented at periodic intervals, e.g., at a frequency of 60 Hz. (onepulse each about 16.67 milliseconds (ms)). An odd/even frame signal Halso is presented; this signal is approximately a square wave havinghigh and low half cycle portions, each half cycle occurring over aperiod of about 16.67 ms. The high portion of the frame signalrepresents an odd or even frame, and low represents the other frame. Avideo data delay signal I controls delivery of video data; high is onand low is off.

In the display system 203 there are two surface mode liquid crystalcells 211 v, 211 h, hereinafter sometimes abbreviated SMD (for surfacemode device), which serve as respective polarization rotators or opticalswitches. It will be evident that other types of switches may be used.As is known, one type of operation of an SMD results in the SMD havingtwo states, one in which it provides substantially no optical phaseretardation of light, for example, zero or near zero, and one in whichit provides a relative maximum amount of optical phase retardation, forexample, 90 degrees, 45 degrees, etc., depending on the opticalthickness of the SMD and/or on other properties of the particular SMD.Usually the minimum and maximum optical phase retardations are produced,respectively, when a respective relative maximum and minimum voltage isapplied across the liquid crystal cell forming the SMD. Usually, theminimum voltage is a non-zero rms voltage which preconditions the liquidSMD crystal cell, sometimes referred to as biasing the SMD, to helpmaintain the alignment of the liquid crystal material in the maximumoptical retardation condition. In one example, the preconditioning isprovided by a constantly applied voltage in the “low voltage” or maximumoptical retardation state. In another example, the precondition isprovided by the effect of an rms voltage occurring as a result ofperiodically driving the liquid crystal cell with a voltage that variesbetween an instantaneous value of a maximum level and zero. In thiscase, the voltage is reapplied before the liquid crystal cell can relaxfully. Other techniques for driving an SMD also may be possible.

As is seen in curve J, the voltage waveform applied to the SMD 211 v(FIG. 14) varies at the extremes J′ between −15 volts and +15 voltswhich provides minimal optical phase retardation (rotation of the planeof polarization). Portions J″ of the voltage J also are at plus andminus a small voltage that is slightly above and below, respectively,the zero voltage level; these portions J″ are the voltage of the SMDwhen it is in the maximum optical phase retardation condition (providingmaximum rotation of plane of polarization). Each portion J′ and J″ ofthe voltage J is the same duration as the respective half cycle of theodd/even signal H and the same duration as the time period betweenvertical sync pulses G. However, the phase of the voltage waveform J isshifted from the phase of the vertical sync G and odd/even frame signalH by an amount which is determined in the manner described above withrespect to FIGS. 44-46, for example. That phase shift in the illustratedexample is 13.2 milliseconds, as is evident from the scale at the bottomof FIG. 48. Waveform signal or voltage K in FIG. 48 is applied to theSMD 211 h (FIG. 14). It varies only at one half (½) the frequency of thewaveform J.

As an example of operation of the display system 203, which is notnecessarily coordinated with the sequence of FIGS. 16A-16D, althoughproducing the result of FIG. 17, incident plane polarized light isprovided to and transmitted through the SMD's 211 h and 211 v, which areoperated generally according to the waveforms J and K. Therefore, thepolarization of light respectively entering the birefringent crystals,e.g., calcite or other birefringent material, 210 h, 210 v will varygenerally in the manner depicted by curves L and M, which issynchronized and in phase or approximately in phase with the operationof the SMD's 211 h, 211 v. As light transmits through the respectivebirefringent crystals 210 h, 210 v, the location of the image fromrespective pixels of the display 202 will vary generally along the linesof the curves N and O. The description herein refers to direction, e.g.,horizontal and vertical; it will be appreciated that such reference onlyis exemplary, and where vertical shifting or orientation is referred to,horizontal could be substituted, and vice versa.

The phase shifting for coordination of optical switching with an opticaldisplay, for example, as described above, also may be used in a displaysystem that provides multicolor output with good contrast even thoughbrightness or intensity of the output light is varied, for example, ofthe type disclosed in above-referenced patent application Ser. No.08/187,163. Using such phase shifting in coordination with the liquidcrystal display system of such patent application and/or with thedithering of others of the patent applications referenced above toprovide a multicolor output can increase the resolution, sharpness andcrispness of the viewed image, for example.

Referring to FIG. 49, a light transmissive display system according toan embodiment of the invention is illustrated at 901. The display system901 includes a light source 902, liquid crystal display 903, such asthat shown at 724 d in FIG. 43, optics 904, such as that shown at 14 inFIG. 43, for projection or viewing of the images created by the liquidcrystal display, a computer control 905, such as the control 729 in FIG.43, and an image signal source 906, which may be part of the control 905or a separate source of video signals or other signals as may beappropriate. A photo detector 907 also may be included in the system901.

The light source 902 may be one or more light emitting diodes,incandescent light source, fluorescent light source, light received viafiber optics or other means, a metal halide lamp, etc.

The liquid crystal display 903 may be a twisted nematic liquid crystalcell, a variable birefringence liquid crystal cell, a supertwist liquidcrystal cell, or some other type or liquid crystal cell able to modulatelight. The liquid crystal display 903 may include polarizers, waveplates, such as quarter wave plates or other wave plates, means forcompensating for residual birefringence or for problems encounteredduring off axis viewing, etc. Other types of display devices whichmodulate light as a function of some type of controlled input can beused in place of the liquid crystal cell 903. Exemplary liquid crystalcells and display devices which may be used for the liquid crystal cell903 are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243, Re.32,521, and 4,582,396, which disclose surface mode and pi-cell liquidcrystal devices, and in concurrently filed, commonly owned U.S. patentapplication Ser. No. 08/187,050, entitled “Folded Variable BirefringenceLiquid Crystal Apparatus.”

The optics 904 may be one or more lenses separate from and/or includedas part of the liquid crystal display for the purpose of providing anoutput image for viewing or for projection. If for viewing, such optics904 may be one or more lenses which focus an image for close, e.g., asin a head mounted display of the heads up display type, virtual realitytype or multimedia type, or far viewing, e.g., as in a slide viewer or atelevision. If for projection, such optics 904 may include projectionoptics which project an image formed by the display 903 onto a screenfor transmissive viewing or reflective viewing.

The image signal source 906 may be a source of computer graphicssignals, NTSC type television (video) signals, or other signals intendedto produce an image on the display 903. Such signals are decoded inconventional manner by the computer control 905, for example, as is thecase in many display systems, and in response to such decoding ordeciphering, the computer control 905 (or some other appropriatecontrol, circuit, etc.) operates the display 903 to produce desiredimages. If desired, the computer control 905 can operate the display 903in sequential manner to produce multiple images in sequence while thedisplay is being illuminated by only a single light source or color oflight, e.g., a monochromatic type of operation. Exemplary operation ofthis type is summarized in the above '396 patent. Other exemplary typesof operation of the computer control 905 include those employed inconventional liquid crystal display televisions of the hand-held orlarger type and/or liquid crystal type computer monitors. Alternatively,the computer control can operate the display 903 in a field sequentialor frame sequential manner whereby a particular image is formed inseveral parts; while one part is formed, the display is illuminated bylight of one color; while another part is formed, the display isilluminated by light of a different color; and so on. Using this fieldsequential type operation, multicolor images can be produced by thedisplay system apparatus 901.

In a typical input signal to a television or liquid crystal television,there is information indicating brightness of the light to betransmitted (or reflected) at a particular pixel. The computer control905 is operative to compute the brightness information of a particularimage or scene and in response to such computation to control theintensity or brightness of the light source 902. While intensity orbrightness of the light source is controlled in this manner, thecomputer control 905 operates the liquid crystal display 903 to modulatelight without having to reduce the number of pixels used to transmitlight. Therefore, the full number or a relatively large number of pixelscan be used to form the image or scene even if the brightness of thescene as controlled by the controlled light source is relatively dark.

Information coming through from the image signal source 906 may indicatevarious levels of illumination. There usually is a blanking pulse and adata line pulse. The computer control 905 can take the integral of thedata line electrically or an integral of the whole set of data (from allof the data lines of the scene) or all of the pixels while electricallyskipping the blanking. Based on that integral, the brightness of thelight incident on the display 903 is controlled by the computer control905. It will be appreciated that a person having ordinary skill in theart would be able to prepare an appropriate computer program to providethe integral functions and to use the results of such integration toprovide brightness control for the light source 902.

From the foregoing, then, it will be appreciated that the apparatus 901,including the computer control 905, is operative to control or to adjustthe brightness of a scene without degrading the contrast ratio. Thus,the same contrast ratio can be maintained while brightness of a scene orimage is adjusted. For example, the same contrast ratio or substantiallythe same contrast ratio can be maintained by the apparatus 901, whetherdepicting a scene of a bright sunlit environment or of the inside of adark cave. Therefore, the scene will have the appearance of illuminationunder natural illumination conditions.

The features of the invention described below can be used in virtuallyany passive display system.

Power requirements of the apparatus 901 can be reduced over priordisplay systems because the intensity of light produced by the source902 is controlled to create dark images. In prior systems, though, theintensity of the light produced by the source was maintainedsubstantially constant while the amount of light permitted to betransmitted through the passive display would be reduced to create adark scene image.

In addition to controlling intensity of the light source 902 as afunction of brightness of a scene, the computer control 905 also may beresponsive to measurement or detection of the ambient environment inwhich the apparatus 901 is located. The brightness of such ambientenvironment may be detected by the photo detector 907. The photodetector 907 may be place in a room or elsewhere where the image createdby the display 903 is to be viewed; and the brightness of the source 902can be adjusted appropriately. For example, if the room is dark, itusually is desirable to reduce brightness of the source; and if the roomis bright or the apparatus is being used in sunlight, the brightness ofthe source may be increased.

Turning to FIG. 50, a light reflective display system according to theinvention is illustrated at 901′. The display system 901′ includes alight source 902′, liquid crystal display 903′, optics 904′ forprojection or viewing of the images created by the liquid crystaldisplay 903′, a computer control 905′, and an image signal source 906. Aphoto detector 907 also may be included in the system 901. The variousparts of the display 903′ and optics 904′ may be the same or similar tothose disclosed in the U.S. patent applications referred to above. Thelight source 902′ and display 903′ may be of the type disclosed inconcurrently filed, commonly owned U.S. patent application Ser. No.08/187,262, entitled “Illumination System For A Display.”

For example, the light source 902′ may include a source of circularlypolarized light 902 a′ and a cholesteric liquid crystal reflector 908.The liquid crystal display 903′ may be a reflective variablebirefringence liquid crystal display device.

Full Color Frame Sequential Illumination System and Display.

Turning to FIG. 51 a full color display subsystem 919 includingillumination system 920 is shown. However, in the display subsystem 919the illumination system 920 includes several sources of light, eachhaving a different wavelength. For example, three separate light sources902 r, 902 g, 902 b provide red, green and blue wavelength light,respectively, or light that is in respective wavelength bands or rangesthat include red, green and blue, respectively. The light sources may berespective light emitting diodes or they may be other sources of red,green and blue light or other respective wavelengths of light, as may bedesired for use in the display subsystem 919. The cholesteric liquidcrystal reflector 908 is able to reflect green light; the reflector 908a is able to reflect red light; the reflector 908 b is able to reflectblue light. Such reflection occurs when the circular polarizationcharacteristic of the light is the same direction as the twist directionof the cholesteric liquid crystal material in the respective reflector.The reflectors 908, 908 a, 908 b are transparent to the otherpolarizations of incident light and to the other wavelengths of incidentlight.

The illumination system 920 is intended sequentially to illuminate thedisplay 903′, which may include a wave plate, such as a quarter waveplate, (or respective portions of the display) with respectivewavelengths of light. For example, for a period of time the display 903′(or portion thereof) is illuminated with red light; subsequentlyillumination is by either green or blue light; and still subsequentlyillumination is by the other of green or blue light. Such sequentialillumination may be carried out sufficiently rapidly so that respectivered, green and blue images created by the display 903′ when illuminatedby the respective colors of light are output from the display subsystem961 and are integrated by the human eye. As a result, the human eyeeffectively sees a multicolor image. Other examples of frame sequentialswitching to provide multicolor and/or full color outputs are known inthe art. Various advantages inure to a frame sequential multicolordisplay, including the ability to provide high resolution withapproximately one-third the number of picture elements required for afull color r, g, b display system in which respective pixels are red,green or blue.

The sequential delivering of red, green and blue light to the display903′ is coordinated by the control system 905 with the driving of thedisplay 903′. Therefore, when a red image or a portion of a red image isto be produced by the display 903′, it is done when red light isincident on the display 903′; and the similar type of operation occurswith respect to green and blue images.

If the respective light sources 902 r, 902 g, 902 b are light emittingdiodes, they may be sequentially operated or energized to provide lightin coordination with the operation of the display 903′ under directcontrol and/or energization by the control system 905. Alternatively,the control system 905 may be coordinated with whatever other means areused to provide the respective red, green and blue color lights of thelight source.

Another example of frame sequential or field sequential operation of adisplays subsystem like that shown at 961 herein is described in theabove-referenced patent applications. Another example of fieldsequential operation is described in U.S. Pat. No. 4,582,396, which ismentioned above and incorporated by reference.

Referring to FIG. 52, a head mounted display 960 includes a pair ofdisplay systems 961, 962 and a control system 705 for creating imagesintended to be viewed by the eyes 964, 965 of a person. The displaysystems 961, 962 may be positioned in relatively close proximity, forexample, at approximately one inch distance, to the respective eyes 964,965. A mounting mechanism, such as temple pieces 966, 967 and a nosebridge 968 may be provided to mount the display 960 on the head of theperson.

The control system 905 in conjunction with the display systems 961, 962are intended to create images for viewing by the eyes. Those images maybe monochromatic. The images may be multicolor. The images may betwo-dimensional or they may provide a three dimensional, stereoscopiceffect. Stereoscopic effect viewing is obtained when the control system905 operates the display systems 961, 962 to provide, respectively,right eye and left eye images that are sufficiently distinct to providedepth perception. Right eye, left eye imaging and depth perception aretechniques used in some stereoscopic imaging and viewing systems whichare commercially available.

The display systems 961, 962 may be identical. The control system 905provides control and/or power input to the display systems 961, 962 tocreate images for display to the eyes 964, 965. The display 960 may be ahead mounted display, such as a heads-up display, a virtual realitydisplay, or a multimedia display. The control system 905 may begenerally a control system of the type used in known head mounteddisplays to create such images. Such a control system may provide forcontrol of color, light intensity, image generating, gamma, etc. Thedisplay systems 961, 962 may include focusing optics so as to focus theimage created by the display systems for comfortable viewing, forexample from a few inches up to a few feet in front of the eyes, say,from about 20 inches to about several feet in front of the eyes.

It will be appreciated that the features of the liquid crystal cell 903′may be used in the display 960 of the head mounted type. Also, featuresof the invention may also be employed in other types of display systems.One example is a display system that uses only a single display systemof the type described herein. Such display system may be located inproximity to an eye for direct viewing. Alternatively, such displaysystem may be used as part of a projection type display in which lightfrom the display system is projected onto a surface where the image isformed for viewing. Various lenses and/other optical components may beused to direct from the display system light to create an appropriateimage at a desired location.

Turning to FIGS. 53-58, operation of the apparatus is described. In FIG.53, a plan view of a dot matrix liquid crystal display is shown. Theshade of grey measured at several pixels is indicated. According to thebottom graph in FIG. 53, the actual shade is shown; according to the dotmatrix image at the side and top of FIG. 53, the actual shade of thepixel is shown. Thus, at location 1 on the graph at the bottom of FIG.53, there is a shade 2. At location 2, there is a shade 1. At location 3there is a shade 0, and so on. In pixel 1 marked in the top of FIG. 53,the pixel is a shade of gray of 2; and at the adjacent pixel the pixelis a shade gray of 1, and so on. This is conventional. This wouldindicate the signals coming in to the computer control 905.

In FIG. 54, an example of a bright image scene produced by back light ata medium (normal) illumination level is illustrated at the top; theshades of gray are shown at the middle left; and the lamp light level isconstant at the bottom left. The viewer sees a bright/low contrast imageof a person as seen at the top right of the drawing. A side view of thedisplay representing respective pixels and the gray levels thereof isshown at the bottom right of the figure.

FIG. 55 is similar to FIG. 54 again with average constant lamp lightlevel. The average light level is produced; the average brightnessoutput from the display is to be produced; and the viewer sees anaverage brightness high contrast image because all conditions areoptimized.

FIG. 56 is similar to FIG. 54 again with average constant lamp lightlevel and a dark transmission provided by the liquid crystal cell; theviewer sees a dim low contrast image.

FIGS. 54-56 represent operation of a standard display apparatus. FIGS.57 and 58 represent applying the principles of the present invention todevelop high contrast images. In FIG. 57 it is seen that there is theintent to produce a wide range of gray levels; and this is possible byusing a high intensity lamp level; the result is a bright high contrastimage. In FIG. 58 it is intended that the viewer see a dim image; thesame range of grey shades are provided as is depicted in the middle leftgraph of the drawing; but the lamp level is low. Therefore, there is agood contrast ratio provide to the viewer; from 0 to about 7 at thebrightness level shown in the graph at the upper left of the drawing.

CHART I CALC3 SHIFT POL POL ¼ × DOUBLES VOLT. DIR CALC1 VOLT DIR CALC2POL DIR HORIZ FRAME FIELD SMD1 OUT1 SHIFT SMD2 OUT2 SHIFT OUT ÷ 2 PIXEL1 1 Lo H None Lo V None H, V ×2 1 2 Hi V Vert. Hi V Non H, V ×2 Down 2 1Lo H None Hi H Horiz. H, V ×2 Right 2 2 Hi V Vert. Lo H Horiz. H, V ×2Down Right

1. A display apparatus, comprising a passive display; a light source toprovide illumination of the passive display a video signal input,wherein in response to a video signal the passive display modulateslight from the light source to provide an image, and wherein theintensity of light provided by the light source illuminating the displayis controlled based on the video signal and wherein the passive displayis capable of displaying a preset range of gray levels and presenting adisplayed image in response to the video signal; and a control operableto expand a range of gray levels represented in the video signal acrosssubstantially all of preset range of gray levels.
 2. The apparatus ofclaim 1, characterized in that the passive display comprises a liquidcrystal display.
 3. The apparatus of claim 1, characterized in that thepassive display comprises a flat panel display.
 4. The apparatus ofclaim 1, characterized in that the passive display is a video monitor.5. The apparatus of claim 1, characterized in that the passive displayis a projection display.
 6. The apparatus of claim 4, furthercharacterized in that the projection display includes projection optics.7. The apparatus of claim 1, characterized in that the passive displayis a direct view display.
 8. The apparatus of claim 7, furthercharacterized in comprising optics to provide the image for viewing fromthe direct view display.
 9. The apparatus of claim 1, characterized inthat the passive display does not produce its own illumination.
 10. Theapparatus of claim 1, wherein the light source is capable to provideplural colors of light to illuminate the display, and furthercharacterized in the control comprising a control to control one or moreof color, intensity, and gamma.
 11. The apparatus of claim 10, furthercharacterized in that the light source comprises plural light sources,at least two of which provide different color light.
 12. A displayapparatus in which light from a light source illuminates a passivedisplay to provide an image, characterized in that the intensity of thelight illuminating the display is controllable to adjust imagebrightness; and the passive display is capable of displaying a presetrange of gray levels and presenting a displayed image in response to thevideo signal; and a range of gray levels represented in the input signalless than the preset range of gray levels is capable of being expandedto display the image.
 13. The apparatus of claim 12, furthercharacterized in that the light source is selected from the groupcomprising a light emitting diode light source, incandescent lightsource, fluorescent light source, fiber optics, and a metal halide lamp.14. The apparatus of claim 12, further characterized in comprising animage source to provide a video signal for the passive display, theimage source including at least one of computer graphics signals andvideo signals.
 15. The apparatus of claim 12, further characterized inthat a computer is used to produce the desired images.
 16. The apparatusof claim 12, further characterized in that the light source iscontrolled to provide scenes having appearance as though illuminatedunder natural illumination conditions.
 17. A method of improving dynamicrange of a passive display operable in response to a video signal incombination with an illuminating light source to display an image andcapable of displaying a preset range of gray levels, the illuminatinglight source being capable of modulation, comprising sampling the videosignal for image brightness information; expanding a range of graylevels represented in the video signal across substantially all of thepreset range of gray levels; and adjusting the intensity of theilluminating light source.
 18. The method of claim 17, characterized inthat said adjusting the intensity comprises adjusting the intensity ofthe light source to correspond with image brightness characteristics.19. The method of claim 17, characterized in that said samplingcomprises computing image brightness of at least a portion of an imagerepresented by such video signal.
 20. The method of claim 17, whereinthe passive display is a transmissive liquid crystal display, andfurther characterized in comprising directing input light through thepassive display to display an image.
 21. A method of optimizingoperation of a display system that includes a light source and a lightmodulating device capable of displaying a preset range of gray levels tomodulate light received from the light source to provide images ofscenes represented by a range of gray levels less than the preset rangeof gray levels in an input signal , comprising controlling the intensityof light produced by the light source as a function of brightness of ascene, whereby for relatively brighter scenes and relatively darkerscenes, the intensity of light produced by the light source is,respectively, relatively higher and relatively lower; and expanding arange of gray levels represented in the input signal acrosssubstantially all of the preset range of gray levels.
 22. A displaysystem including a display for modulating light from an illuminatingsource in response to a signal to provide a displayed image, theilluminating source being capable of modulation, comprising means forsampling the signal for image brightness information, means formodifying the signal to optimize contrast in the image by expanding arange of gray levels represented in the signal across substantially allof a preset range of gray levels, and means for adjusting theilluminating source to set the brightness of the display insynchronization with the presentation of the image.
 23. The displaysystem of claim 22, further characterized in that the optimization iscarried out within the capability of the display system.
 24. The displaysystem of claim 22, further characterized in that said signal is a videosignal including image brightness information.
 25. The display system ofclaim 22, further characterized in that said means for adjustingcomprises means for adjusting the intensity of the light source tocorrespond with image brightness characteristics, and said means formodifying the signal comprises means for altering image brightnesscharacteristics in synchronism with the displayed image.
 26. The displaysystem of claim 25, wherein altering image brightness characteristicsincludes expanding a range of gray levels representing the image.
 27. Adisplay system comprising a display for modulating light from anilluminating source in response to a signal to provide a displayedimage, wherein the illuminating source is capable of modulation, asampling device sampling the signal for image brightness information, acircuit modifying the signal to optimize contrast in the image byexpanding a range of gray levels representing the image acrosssubstantially all of a preset range of gray levels, and adjusting deviceoperable to adjust the illuminating source to set the brightness of thedisplay in synchronization with the presentation of the image.
 28. Amethod of improving dynamic range of a passive display operable inresponse to a video signal in combination with an illuminating lightsource to display an image, the illuminating light source being capableof modulation, characterized in sampling the video signal for imagebrightness information; adjusting the video signal for improved contrastby expanding a range of gray levels represented in the video signalacross substantially all of a preset range of gray levels; and adjustingthe intensity of the illuminating light source for improved brightnessall in synchronization with the display.
 29. The method of claim 28,characterized in that said adjusting the intensity comprises adjustingthe intensity of the light source to correspond with image brightnesscharacteristics, and said adjusting the video signal comprises expandinga range of gray levels representing the image.
 30. The method of claim29, wherein the display is a liquid crystal display, and furthercharacterized in that the adjusted video signal is provided to theliquid crystal display to affect light transmission or reflectioncharacteristics of respective picture elements (pixels) of the liquidcrystal display.
 31. The method of claim 28, characterized in that saidsampling comprises computing image brightness of at least a portion ofan image represented by such video signal.
 32. The method of claim 28,wherein the passive display is a transmissive liquid crystal display,and further characterized in comprising directing input light throughthe passive display to display an image.
 33. The method of claim 28,wherein the display modulates input light from the light source that iscapable of independently controlling intensity of color components oflight to provide displayed images, further characterized in computingbrightness information of an image or scene from the input signalpertaining to the image or scene; and adjusting the light source andgray range for color and intensity to recover the relative brightness ofa natural scene represented by the image; said computing and adjustingbeing all in synchronization with the displayed video images.
 34. Themethod of claim 33, further characterized in that said adjusting thelight source is carried out independently for different respective red,green and blue colors at video rates.
 35. The method of claim 33,wherein the light source is comprised of respective light emittingdiodes, and further characterized in that said adjusting the lightsource comprises independently adjusting respective diodes.
 36. A methodof reducing power consumption of a display apparatus, the displayapparatus comprising a controller, a passive display device, and abacklight, the method comprising: sensing brightness levels and range ofgray levels of an input image signal; and decreasing intensity of lightfrom the backlight when the brightness level of the input image signalis dim while increasing transmission of the passive display panel byexpanding the range of gray levels in a displayed image to be greaterthan the range of gray levels of the input image signal.
 37. The methodof reducing power consumption of claim 36, further comprising furtherdecreasing the intensity of light from the backlight if the ambientlight level of a surrounding environment is low.
 38. A method ofoperating a display system that includes a light source and a passivedisplay device to modulate light received from the light source toprovide images of scenes represented in an input image signal, themethod comprising: adjusting gamma of the passive display device; andcontrolling the intensity of light produced by the light source as afunction of brightness of a scene, whereby for relatively brighterscenes and relatively darker scenes, the intensity of light produced bythe light source is, respectively, relatively higher and relativelylower, wherein such control corresponds to the adjusting gamma of thepassive display device.
 39. The method of claim 38, further comprising:sampling the input image signal for scene brightness information; andadjusting gamma of the passive display device based on the scenebrightness information.
 40. The method of claim 38, further comprising:sampling the input image signal for scene brightness information andcolor information; and adjusting gamma of the passive display devicebased on the scene brightness information and color information.
 41. Amethod of operating a display system that includes a light source and apassive display device to modulate light received from the light sourceto provide images of scenes represented in an input image signal, thepassive display device being capable of displaying a preset range ofgray levels, the method comprising: sampling the input image signal forscene brightness information; adjusting a distribution of gray levelsrepresented in the input image signal; and controlling the intensity oflight produced by the light source as a function of brightness of ascene, whereby for relatively brighter scenes and relatively darkerscenes, the intensity of light produced by the light source is,respectively, relatively higher and relatively lower, wherein suchcontrol of intensity corresponds to the adjusting the distribution ofgray levels.